| Occult Academy | July 5, 2010 | — | 13 |
| Occultic;Nine | October 9, 2016 | — | 12 |
| Octonauts | September 16, 2010 | British Broadcasting Corporation, CBeebies | 133 |
| Octonauts: Above & Beyond | September 7, 2021 | Netflix | 13 |
| Oda Cinnamon Nobunaga | January 10, 2020 | — | 12 |
| Odd Family | 2002 | TF1 | 26 |
| Odd Job Jack | March 5, 2003 | CTV Comedy Channel | 52 |
| Odd Taxi | April 6, 2021 | TV Tokyo | 13 |
| Oddballs | October 7, 2022 | Netflix | 20 |
| Oddbods | 2013 | Disney Channel Asia | 260 |
| Odekake Kozame | August 1, 2023 | — | 60 |
| Oedo Fire Slayer: The Legend of Phoenix | January 12, 2026 | — | 12 |
| Offside | May 10, 2001 | — | 39 |
| Ogenki Clinic | July 20, 1991 | — | 3 |
| Oggy and the Cockroaches | November 28, 1998 | Gulli, France 3 | 501 |
| Oggy and the Cockroaches Next Generation | November 8, 2021 | Gulli | 13 |
| Ogre Slayer | September 9, 1994 | — | 4 |
| Oh Boy, Was I Wrong About Her | July 6, 2026 | — | 12 |
| Oh My Goddess! | — | — | 5 |
| Oh My Goddess! | January 6, 2005 | TBS Television | — |
| Oh My Goddess! | February 23, 2011 | — | 3 |
| Oh My School! | — | — | — |
| Oh Yeah! Cartoons | July 18, 1998 | Nickelodeon | 75 |
| Oh Yuck! | 2017 | — | — |
| Oh! Edo Rocket | April 3, 2007 | — | 26 |
| Oh! Family | October 6, 1986 | TV Tokyo | 26 |
| Oh! My Goddess: The Adventures of Mini-Goddess | April 6, 1998 | — | — |
| Ohayou Hakushon Daimaou | — | — | 237 |
| Ohayō! Spank | March 7, 1981 | — | 66 |
| Ohayō! Unko-sensei | July 26, 2024 | — | — |
| Oi! Ryoma | April 7, 1992 | NHK General TV | 39 |
| Oishi High School Battle | — | — | 30 |
| Oishinbo | October 17, 1988 | — | 136 |
| Ojamajo Doremi | February 7, 1999 | — | 201 |
| Ojamajo Doremi: Owarai Gekijō | March 23, 2019 | — | 26 |
| Ojamanga Yamada-kun | September 28, 1980 | — | 101 |
| Ojarumaru | October 5, 1998 | NHK Educational TV | 1,868 |
| Ojisan and Marshmallow | January 7, 2016 | — | 12 |
| OK K.O.! Let's Be Heroes | August 1, 2017 | Cartoon Network | 112 |
| Okama Report | March 12, 1991 | — | 3 |
| Okami-san and Her Seven Companions | July 1, 2010 | — | 12 |
| Okawari-Boy Starzan S | January 7, 1984 | Fuji Television | 34 |
| Okitsura | January 5, 2025 | — | 12 |
| Okojo-san | October 2, 2001 | TV Tokyo | 51 |
| Oku-sama wa Joshi Kōsei | July 2, 2005 | Television Kanagawa | 13 |
| Oku-sama wa Mahō Shōjo: Bewitched Agnes | July 3, 2005 | — | 13 |
| Old Tom | 2002 | ABC Television | 52 |
| Olive the Ostrich | 2011 | Nick Jr. Channel | 104 |
| Olivia | January 24, 2009 | Nick Jr. | 37 |
| Ollie's Pack | April 6, 2020 | Nickelodeon | 27 |
| Olympics with Bolek and Lolek | — | Telewizja Polska | 13 |
| Olympus Guardian | December 11, 2002 | Seoul Broadcasting System | — |
| Om Nom Stories | — | Rovio Entertainment, CITV | 39 |
| Omae wa Mada Gunma o Shiranai: Reiwa-ban | January 10, 2026 | — | 12 |
| Omae, Tanuki ni Naranee ka? | — | — | — |
| Omakase Scrappers | April 7, 1994 | NHK Satellite 2 Television | — |
| Omakase! Miracle Cat-dan | March 31, 2015 | NHK Educational TV | 32 |
| Omamori Himari | January 6, 2010 | — | 12 |
| Omar & Hana | — | — | — |
| Omishi Magical Theater: Risky Safety | October 5, 1999 | WOWOW | 24 |