Japan competed at the 2013 World Aquatics Championships in Barcelona, Spain between 19 July and 4 August 2013.

Japan qualified four quota places for the following diving events:^[1]

Men

Women

Japan qualified three quota places for the following events in open water swimming:^[2]

Japanese swimmers achieved qualifying standards in the following events (up to a maximum of 2 swimmers in each event at the A-standard entry time, and 1 at the B-standard):^[3][4] Among the official roster featured former Olympic champion Kosuke Kitajima and undisputed superstar Kosuke Hagino.^[5]

Men

More information Athlete, Event ...

Athlete	Event	Heat		Semifinal		Final
		Time	Rank	Time	Rank	Time	Rank
Takuro Fujii	100 m butterfly	52.50	15 Q	52.27	13	Did not advance
Kosuke Hagino	200 m freestyle	1:47.33	4 Q	1:46.87	3 Q	1:45.94	5
	400 m freestyle	3:46.92	4 Q	—		3:44.82 NR
	100 m backstroke	53.94	7 Q	53.68	6 Q	53.93	6
	200 m backstroke	1:57.52	7 Q	1:56.24	4 Q	1:55.43	5
	200 m individual medley	1:57.73	2 Q	1:57.38	2 Q	1:56.29
	400 m individual medley	4:13.80	4 Q	—		4:10.77	5
Ayatsugu Hirai	800 m freestyle	7:56.69	14	—		Did not advance
	1500 m freestyle	15:03.45	9	—		Did not advance
Ryosuke Irie	50 m backstroke	DNS		Did not advance
	100 m backstroke	53.66	4 Q	53.41	4 Q	53.29	4
	200 m backstroke	1:57.53	8 Q	1:56.14	=3 Q	1:55.07	4
Kenta Ito	50 m freestyle	22.77	28	Did not advance
	100 m freestyle	49.91	=31	Did not advance
Kosuke Kitajima	50 m breaststroke	27.43	9 Q	27.82	15	Did not advance
	100 m breaststroke	59.88	=3 Q	59.92	8 Q	59.98	6
Yuki Kobori	100 m butterfly	53.11	=25	Did not advance
	200 m butterfly	1:56.64	8 Q	1:56.15	9	Did not advance
Takeshi Matsuda	200 m butterfly	1:57.14	11 Q	1:56.42	11	Did not advance
Yōsuke Miyamoto	1500 m freestyle	15:09.21	=12	—		Did not advance
Daiya Seto	200 m individual medley	1:59.25	12 Q	1:58.03	6 Q	1:58.45	7
	400 m individual medley	4:12.96	2 Q	—		4:08.69
Shinri Shioura	50 m freestyle	22.02	10 Q	22.04	15	Did not advance
	100 m freestyle	48.52	4 Q	48.51	10	Did not advance
Ryo Tateishi	200 m breaststroke	2:10.41	6 Q	2:10.01	8 Q	2:10.28	8
Akihiro Yamaguchi	100 m breaststroke	1:00.69	19	Did not advance
	200 m breaststroke	2:10.17	5 Q	2:10.00	7 Q	2:09.57	7
Takuro Fujii Kenta Ito Kenji Kobase Shinri Shioura	4×100 m freestyle relay	3:15.46	8 Q	—		3:14.75	8
Kosuke Hagino Yuki Kobori Takeshi Matsuda Daiya Seto* Sho Sotodate	4×200 m freestyle relay	7:09.98	3 Q	—		7:04.95	5
Takuro Fujii Ryosuke Irie Kosuke Kitajima Shinri Shioura	4×100 m medley relay	3:34.25	5 Q	—		3:32.26

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Women

More information Athlete, Event ...

Athlete	Event	Heat		Semifinal		Final
		Time	Rank	Time	Rank	Time	Rank
Sayaka Akase	100 m backstroke	1:02.51	28	Did not advance
	200 m backstroke	2:10.87	13 Q	2:11.48	13	Did not advance
Natsumi Hoshi	100 m butterfly	59.18	=16 Q*	59.42	16	Did not advance
	200 m butterfly	2:07.59	3 Q	2:07.18	=4 Q	2:06.09	4
Chihiro Igarashi	200 m freestyle	1:59.00	17	Did not advance
	400 m freestyle	4:12.44	15	—		Did not advance
Rie Kaneto	50 m breaststroke	32.37	34	Did not advance
	200 m breaststroke	2:23.91	4 Q	2:23.28	5 Q	2:22.96	4
Yayoi Matsumoto	50 m freestyle	25.69	25	Did not advance
Miyu Otsuka	200 m backstroke	2:11.69	14 Q	2:11.68	14	Did not advance
	400 m individual medley	4:37.77	8 Q	—		4:39.21	8
Satomi Suzuki	50 m breaststroke	DNS		Did not advance
	100 m breaststroke	1:07.79	11 Q	1:07.83	12	Did not advance
	200 m breaststroke	2:27.31	11 Q	2:25.77	11	Did not advance
Miho Takahashi	400 m individual medley	4:45.70	18	—		Did not advance
Aya Terakawa	50 m backstroke	28.05	3 Q	27.70	2 Q	27.53
	100 m backstroke	1:00.09	7 Q	59.80	4 Q	59.23
Miho Teramura	200 m individual medley	2:12.91	12 Q	2:14.02	14	Did not advance
Haruka Ueda	100 m freestyle	55.78	28	Did not advance
Kanako Watanabe	100 m breaststroke	1:09.28	26	Did not advance
	200 m individual medley	2:12.28	9 Q	2:11.50	11	Did not advance
Yayoi Matsumoto Miki Uchida Haruka Ueda Misaki Yamaguchi	4×100 m freestyle relay	3:39.24	8 Q	—		3:39.45	7
Chihiro Igarashi Yasuko Miyamoto Aya Takano Haruka Ueda	4×200 m freestyle relay	7:56.98	7 Q	—		7:58.15	8
Natsumi Hoshi Satomi Suzuki Aya Terakawa Haruka Ueda	4×100 m medley relay	4:00.18	5 Q	—		3:58.06	5

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Japan qualified 11 quota places for each of the following synchronized swimming events.^[6]