diff --git a/common.mk b/common.mk
index da4608bc61..71dcbf477c 100644
--- a/common.mk
+++ b/common.mk
@@ -781,8 +781,6 @@ EXT_SRCS = $(srcdir)/ext/ripper/ripper.c \
 
 srcs-ext: $(EXT_SRCS)
 
-srcs-extra: $(srcdir)/ext/json/parser/parser.c
-
 LIB_SRCS = $(srcdir)/lib/unicode_normalize/tables.rb
 
 srcs-lib: $(LIB_SRCS)
@@ -875,11 +873,6 @@ $(srcdir)/ext/ripper/ripper.c: parse.y id.h
 		Q=$(Q) ECHO=$(ECHO) RM="$(RM)" top_srcdir=../.. srcdir=. VPATH="$(PWD)" \
 		RUBY="$(BASERUBY)" PATH_SEPARATOR="$(PATH_SEPARATOR)"
 
-$(srcdir)/ext/json/parser/parser.c: $(srcdir)/ext/json/parser/parser.rl
-	$(ECHO) generating $@
-	$(Q) $(CHDIR) $(@D) && $(exec) $(MAKE) -f prereq.mk $(MFLAGS) \
-		Q=$(Q) ECHO=$(ECHO) top_srcdir=../../.. srcdir=. VPATH=../../.. BASERUBY="$(BASERUBY)"
-
 $(srcdir)/ext/rbconfig/sizeof/sizes.c: $(srcdir)/ext/rbconfig/sizeof/depend \
 		$(srcdir)/tool/generic_erb.rb $(srcdir)/template/sizes.c.tmpl $(srcdir)/configure.in
 	$(ECHO) generating $@
diff --git a/doc/maintainers.rdoc b/doc/maintainers.rdoc
index d657626e30..74ee6aaee0 100644
--- a/doc/maintainers.rdoc
+++ b/doc/maintainers.rdoc
@@ -269,8 +269,6 @@ Zachary Scott (zzak)
   Nobuyuki Nakada (nobu)
 [ext/io/wait]
   Nobuyuki Nakada (nobu)
-[ext/json]
-  NARUSE, Yui (naruse)
 [ext/mathn/complex]
   * 1.8: 1.9 feature
   * 1.9: Keiju ISHITSUKA (keiju)
diff --git a/ext/.document b/ext/.document
index 2e6fc78879..f5da0912ed 100644
--- a/ext/.document
+++ b/ext/.document
@@ -35,9 +35,6 @@ io/console/console.c
 io/nonblock/nonblock.c
 io/wait/lib
 io/wait/wait.c
-json/ext/generator/generator.c
-json/ext/parser/parser.c
-json/lib
 mathn/complex/complex.c
 mathn/rational/rational.c
 nkf/lib
diff --git a/ext/Setup b/ext/Setup
index 05998e3363..2ca8e9ce9e 100644
--- a/ext/Setup
+++ b/ext/Setup
@@ -20,9 +20,6 @@
 #io/console
 #io/nonblock
 #io/wait
-#json
-#json/generator
-#json/parser
 #mathn/complex
 #mathn/rational
 #nkf
diff --git a/ext/Setup.nacl b/ext/Setup.nacl
index f205e367c6..4ef8d3972f 100644
--- a/ext/Setup.nacl
+++ b/ext/Setup.nacl
@@ -22,9 +22,6 @@
 # io/console
 # io/nonblock
 # io/wait
-# #json
-# json/generator
-# json/parser
 # mathn/complex
 # mathn/rational
 # nkf