diff --git a/examples/mpm128.py b/examples/mpm128.py
index 2e7f207080b9e..ffdfdacf3da4a 100644
--- a/examples/mpm128.py
+++ b/examples/mpm128.py
@@ -98,7 +98,7 @@ def reset():
   Jp.fill(1)
   C.fill(0)
   
-print("[Hint] Use WSAD/arrow keys to control gravity. Use left/right mouse bottons to attract/repel. (OS X not yet supported)")
+print("[Hint] Use WSAD/arrow keys to control gravity. Use left/right mouse bottons to attract/repel.")
 gui = ti.GUI("Taichi MLS-MPM-128", res=512, background_color=0x112F41)
 reset()
 
diff --git a/taichi/gui/cocoa.cpp b/taichi/gui/cocoa.cpp
index fc8975b03379b..dd0736565619d 100644
--- a/taichi/gui/cocoa.cpp
+++ b/taichi/gui/cocoa.cpp
@@ -6,6 +6,11 @@
 
 #include <taichi/platform/mac/objc_api.h>
 
+#include <algorithm>
+#include <optional>
+#include <string>
+#include <unordered_map>
+
 // https://stackoverflow.com/questions/4356441/mac-os-cocoa-draw-a-simple-pixel-on-a-canvas
 // http://cocoadevcentral.com/d/intro_to_quartz/
 // Modified based on
@@ -15,6 +20,7 @@
 // https://developer.apple.com/documentation/objectivec/objective-c_runtime?language=objc
 
 #include <ApplicationServices/ApplicationServices.h>
+#include <Carbon/Carbon.h>
 #include <CoreGraphics/CGBase.h>
 #include <CoreGraphics/CGGeometry.h>
 #include <objc/NSObjCRuntime.h>
@@ -23,6 +29,109 @@ namespace {
 using taichi::mac::call;
 using taichi::mac::cast_call;
 using taichi::mac::clscall;
+
+std::string str_tolower(std::string s) {
+  // https://en.cppreference.com/w/cpp/string/byte/tolower
+  std::transform(s.begin(), s.end(), s.begin(),
+                 [](unsigned char c) { return std::tolower(c); });
+  return s;
+}
+
+std::optional<std::string> try_get_alnum(ushort keycode) {
+// Can someone tell me the reason why Apple didn't make these consecutive...
+#define CASE(i) \
+  { kVK_ANSI_##i, str_tolower(#i) }
+  static const std::unordered_map<ushort, std::string> key2str = {
+      CASE(0), CASE(1), CASE(2), CASE(3), CASE(4), CASE(5), CASE(6), CASE(7),
+      CASE(8), CASE(9), CASE(A), CASE(B), CASE(C), CASE(D), CASE(E), CASE(F),
+      CASE(G), CASE(H), CASE(I), CASE(J), CASE(K), CASE(L), CASE(M), CASE(N),
+      CASE(O), CASE(P), CASE(Q), CASE(R), CASE(S), CASE(T), CASE(U), CASE(V),
+      CASE(W), CASE(X), CASE(Y), CASE(Z),
+  };
+#undef CASE
+  const auto iter = key2str.find(keycode);
+  if (iter == key2str.end()) {
+    return std::nullopt;
+  }
+  return iter->second;
+}
+
+std::optional<std::string> try_get_fnkey(ushort keycode) {
+  // Or these...
+#define STRINGIFY(x) #x
+#define CASE(i) \
+  { kVK_F##i, STRINGIFY(F##i) }
+  static const std::unordered_map<ushort, std::string> key2str = {
+      CASE(1),  CASE(2),  CASE(3),  CASE(4),  CASE(5),  CASE(6),
+      CASE(7),  CASE(8),  CASE(9),  CASE(10), CASE(11), CASE(12),
+      CASE(13), CASE(14), CASE(15), CASE(16),
+  };
+#undef CASE
+#undef STRINGIFY
+  const auto iter = key2str.find(keycode);
+  if (iter == key2str.end()) {
+    return std::nullopt;
+  }
+  return iter->second;
+}
+
+std::string lookup_keysym(ushort keycode) {
+  // Full enum definition:
+  // https://github.com/phracker/MacOSX-SDKs/blob/ef9fe35d5691b6dd383c8c46d867a499817a01b6/MacOSX10.6.sdk/System/Library/Frameworks/Carbon.framework/Versions/A/Frameworks/HIToolbox.framework/Versions/A/Headers/Events.h#L198-L315
+  switch (keycode) {
+    case kVK_LeftArrow:
+      return "Left";
+    case kVK_RightArrow:
+      return "Right";
+    case kVK_UpArrow:
+      return "Up";
+    case kVK_DownArrow:
+      return "Down";
+    case kVK_Tab:
+      return "Tab";
+    case kVK_Return:
+      return "Return";
+    // Mac Delete = Backspace on other platforms
+    // Mac ForwardDelete (Fn + Delete) = Delete on other platforms
+    case kVK_Delete:
+      return "BackSpace";
+    case kVK_Escape:
+      return "Escape";
+    case kVK_Shift:
+      return "Shift_L";
+    case kVK_RightShift:
+      return "Shift_R";
+    // Shall we interpret Command key as Ctrl?
+    case kVK_Control:
+      return "Control_L";
+    case kVK_RightControl:
+      return "Control_R";
+    // Mac Option = Alt on other platforms
+    case kVK_Option:
+      return "Alt_L";
+    case kVK_RightOption:
+      return "Alt_R";
+    case kVK_CapsLock:
+      return "Caps_Lock";
+    default:
+      break;
+  }
+  auto val_opt = try_get_alnum(keycode);
+  if (val_opt.has_value()) {
+    return *val_opt;
+  }
+  val_opt = try_get_fnkey(keycode);
+  if (val_opt.has_value()) {
+    return *val_opt;
+  }
+  return "Vk" + std::to_string((int)keycode);
+}
+
+// TODO(k-ye): Define all the magic numbers for Obj-C enums here
+constexpr int NSApplicationActivationPolicyRegular = 0;
+constexpr int NSEventTypeKeyDown = 10;
+constexpr int NSEventTypeKeyUp = 11;
+
 }  // namespace
 
 extern id NSApp;
@@ -113,6 +222,20 @@ void GUI::create_window() {
     fprintf(stderr, "Failed to initialized NSApplication.\nterminating.\n");
     return;
   }
+  // I finally found how to bring the NSWindow to the front and to handle
+  // keyboard events in these posts:
+  // https://stackoverflow.com/a/11010614/12003165
+  // http://www.cocoawithlove.com/2010/09/minimalist-cocoa-programming.html
+  //
+  // The problem was that, a Cocoa app without NIB files (app bundle,
+  // info.plist, whatever the meta files are) by default has a policy of
+  // NSApplicationActivationPolicyProhibited.
+  // (https://developer.apple.com/documentation/appkit/nsapplicationactivationpolicy/nsapplicationactivationpolicyprohibited?language=objc)
+  call(NSApp, "setActivationPolicy:", NSApplicationActivationPolicyRegular);
+  // This doesn't seem necessary, but in case there's some weird bug causing the
+  // Window not to be brought to the front, try enable this.
+  // https://stackoverflow.com/a/7460187/12003165
+  // call(NSApp, "activateIgnoringOtherApps:", YES);
   img_data_length = width * height * 4;
   img_data.resize(img_data_length);
   auto appDelObj = clscall("AppDelegate", "alloc");
@@ -145,14 +268,28 @@ void GUI::process_event() {
       call(NSApp, "sendEvent:", event);
       call(NSApp, "updateWindows");
       auto p = cast_call<CGPoint>(event, "locationInWindow");
+      ushort keycode = 0;
+      std::string keysym;
       switch (event_type) {
         case 1:  // NSLeftMouseDown
           set_mouse_pos(p.x, p.y);
           mouse_event(MouseEvent{MouseEvent::Type::press, cursor_pos});
+          key_events.push_back(
+              GUI::KeyEvent{GUI::KeyEvent::Type::press, "LMB", cursor_pos});
           break;
         case 2:  // NSLeftMouseUp
           set_mouse_pos(p.x, p.y);
           mouse_event(MouseEvent{MouseEvent::Type::release, cursor_pos});
+          key_events.push_back(
+              GUI::KeyEvent{GUI::KeyEvent::Type::release, "LMB", cursor_pos});
+          break;
+        case 3:  // NSEventTypeRightMouseDown
+          key_events.push_back(
+              GUI::KeyEvent{GUI::KeyEvent::Type::press, "RMB", cursor_pos});
+          break;
+        case 4:  // NSEventTypeRightMouseUp
+          key_events.push_back(
+              GUI::KeyEvent{GUI::KeyEvent::Type::release, "RMB", cursor_pos});
           break;
         case 5:   // NSMouseMoved
         case 6:   // NSLeftMouseDragged
@@ -161,6 +298,15 @@ void GUI::process_event() {
           set_mouse_pos(p.x, p.y);
           mouse_event(MouseEvent{MouseEvent::Type::move, Vector2i(p.x, p.y)});
           break;
+        case NSEventTypeKeyDown:
+        case NSEventTypeKeyUp:
+          keycode = cast_call<ushort>(event, "keyCode");
+          keysym = lookup_keysym(keycode);
+          auto kev_type = (event_type == NSEventTypeKeyDown)
+                              ? KeyEvent::Type::press
+                              : KeyEvent::Type::release;
+          key_events.push_back(KeyEvent{kev_type, keysym, cursor_pos});
+          break;
       }
     } else {
       break;