Series beginning with O
- Oakleaf Academy
- Oceanx Adventures
- Oddmire
- The Odds
- Offline Diaries
- Oksa Pollock
- Old Kingdom
- Old Tom
- Olga
- Olga da Polga
- Oli and Skipjack's Tales of Trouble!
- Oliver Moon
- Olivia
- Ollie Spark
- Ology Series
- Olympia
- Olympuss Games
- On the Run
- Once
- Once Upon a Con
- Once We Were Witches
- One and Only Ivan
- One Crazy Summer
- One Dollar Horse
- One Weird Day at Freekham High
- Onyeka
- Opal Cowan
- Opal Moonbaby
- Opie Jones
- Oracle
- Oracle Prophecies
- Orca
- Order of Darkness
- Order of the Majestic
- Order of the Night Jay
- Ordinary Farm
- Orgo Runners
- Origami Yoda
- Orion Chronicles
- Orla
- Orphan Monster Spy
- Orphans of St Halibut's
- Orphans of the Tide
- Otto
- Ottoline
- Our House
- Out of the Hitler Time
- Outernet
- Outlaws of Time
- Outlaws Scarlett and Browne
- Outliers
- Overthrow
- Owl Diaries
- Owls of Blossom Wood
- Owners
- Oz