diff --git a/docs/supportedsites.md b/docs/supportedsites.md
index eed7aa107e..3e088e72a7 100644
--- a/docs/supportedsites.md
+++ b/docs/supportedsites.md
@@ -433,6 +433,12 @@ Consider all sites to be NSFW unless otherwise known.
     <td>Chapters, Manga</td>
     <td></td>
 </tr>
+<tr>
+    <td>MangaSee</td>
+    <td>https://mangasee123.com/</td>
+    <td>Chapters, Manga</td>
+    <td></td>
+</tr>
 <tr>
     <td>Mangoxo</td>
     <td>https://www.mangoxo.com/</td>
diff --git a/gallery_dl/extractor/__init__.py b/gallery_dl/extractor/__init__.py
index d07c063686..d74d06d2f6 100644
--- a/gallery_dl/extractor/__init__.py
+++ b/gallery_dl/extractor/__init__.py
@@ -74,6 +74,7 @@
     "mangakakalot",
     "manganelo",
     "mangapark",
+    "mangasee",
     "mangoxo",
     "myhentaigallery",
     "myportfolio",
diff --git a/gallery_dl/extractor/mangasee.py b/gallery_dl/extractor/mangasee.py
new file mode 100644
index 0000000000..1b3dd18765
--- /dev/null
+++ b/gallery_dl/extractor/mangasee.py
@@ -0,0 +1,112 @@
+# -*- coding: utf-8 -*-
+
+# Copyright 2021 Mike Fährmann
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 2 as
+# published by the Free Software Foundation.
+
+"""Extractors for https://mangasee123.com/"""
+
+from .common import ChapterExtractor, MangaExtractor
+from .. import text
+import json
+
+
+class MangaseeBase():
+    category = "mangasee"
+    browser = "firefox"
+    root = "https://mangasee123.com"
+
+    @staticmethod
+    def _transform_chapter(data):
+        chapter = data["Chapter"]
+        return {
+            "title"   : data["ChapterName"] or "",
+            "index"   : chapter[0],
+            "chapter" : int(chapter[1:-1]),
+            "chapter_minor": "" if chapter[-1] == "0" else "." + chapter[-1],
+            "chapter_string": chapter,
+            "lang"    : "en",
+            "language": "English",
+            "date"    : text.parse_datetime(
+                data["Date"], "%Y-%m-%d %H:%M:%S"),
+        }
+
+
+class MangaseeChapterExtractor(MangaseeBase, ChapterExtractor):
+    pattern = r"(?:https?://)?mangasee123\.com(/read-online/[^/?#]+\.html)"
+    test = (("https://mangasee123.com/read-online"
+             "/Tokyo-Innocent-chapter-4.5-page-1.html"), {
+        "pattern": r"https://[^/]+/manga/Tokyo-Innocent/0004\.5-00\d\.png",
+        "count": 8,
+        "keyword": {
+            "chapter": 4,
+            "chapter_minor": ".5",
+            "chapter_string": "100045",
+            "count": 8,
+            "date": "dt:2020-01-20 21:52:53",
+            "extension": "png",
+            "filename": r"re:0004\.5-00\d",
+            "index": "1",
+            "lang": "en",
+            "language": "English",
+            "manga": "Tokyo Innocent",
+            "page": int,
+            "title": "",
+        },
+    })
+
+    def metadata(self, page):
+        extr = text.extract_from(page)
+        self.chapter = data = json.loads(extr("vm.CurChapter =", ";\r\n"))
+        self.domain = extr('vm.CurPathName = "', '"')
+        self.slug = extr('vm.IndexName = "', '"')
+
+        data = self._transform_chapter(data)
+        data["manga"] = extr('vm.SeriesName = "', '"')
+        return data
+
+    def images(self, page):
+        chapter = self.chapter["Chapter"][1:]
+        if chapter[-1] == "0":
+            chapter = chapter[:-1]
+        else:
+            chapter = chapter[:-1] + "." + chapter[-1]
+
+        base = "https://{}/manga/{}/".format(self.domain, self.slug)
+        if self.chapter["Directory"]:
+            base += self.chapter["Directory"] + "/"
+        base += chapter + "-"
+
+        return [
+            ("{}{:>03}.png".format(base, i), None)
+            for i in range(1, int(self.chapter["Page"]) + 1)
+        ]
+
+
+class MangaseeMangaExtractor(MangaseeBase, MangaExtractor):
+    chapterclass = MangaseeChapterExtractor
+    pattern = r"(?:https?://)?mangasee123\.com(/manga/[^/?#]+)"
+    test = (("https://mangasee123.com/manga"
+             "/Nakamura-Koedo-To-Daizu-Keisuke-Wa-Umaku-Ikanai"), {
+        "pattern": MangaseeChapterExtractor.pattern,
+        "count": ">= 17",
+    })
+
+    def chapters(self, page):
+        slug, pos = text.extract(page, 'vm.IndexName = "', '"')
+        chapters = json.loads(text.extract(
+            page, "vm.Chapters = ", ";\r\n", pos)[0])
+
+        result = []
+        for data in map(self._transform_chapter, chapters):
+            url = "{}/read-online/{}-chapter-{}{}".format(
+                self.root, slug, data["chapter"], data["chapter_minor"])
+            if data["index"] != "1":
+                url += "-index-" + data["index"]
+            url += "-page-1.html"
+
+            data["manga"] = slug
+            result.append((url, data))
+        return result
diff --git a/scripts/supportedsites.py b/scripts/supportedsites.py
index 1bb5d654d2..92e703084f 100755
--- a/scripts/supportedsites.py
+++ b/scripts/supportedsites.py
@@ -68,6 +68,7 @@
     "mangakakalot"   : "MangaKakalot",
     "manganelo"      : "Manganato",
     "mangapark"      : "MangaPark",
+    "mangasee"       : "MangaSee",
     "mangastream"    : "Manga Stream",
     "mastodon.social": "mastodon.social",
     "myhentaigallery": "My Hentai Gallery",