On June 8, 2004, 4Kids Entertainment acquired the license for distribution of One Piece in North America. 4Kids contracted Viz Media to handle home video distribution. 4Kids' in-house musicians wrote a new background score and theme song nicknamed "Pirate Rap". 4Kids' dub mandated edits for content and length, which reduced the first 143 episodes into 104. Initially, 4Kids originally created an English version of the first opening theme, "We Are!" It premiered in the United States on September 18, 2004, in first-run syndication on the Fox network as part of the weekend programming block Fox Box, and later aired on Cartoon Network on their weekday afternoon programming block Toonami in April 2005. Production was halted in 2006 after episode 143 / 104. Viz also ceased its home video release of the series after volume 11. On July 22, 2010, an interview with Anime News Network and Mark Kirk, senior vice-president of digital media for 4Kids Entertainment, revealed that 4Kids acquired One Piece as part of a package deal with other anime, and that the company did not screen the series before licensing it. However, once 4Kids realized One Piece was not appropriate for their intended demographic, the company decided to edit it into a more child-oriented series until they had an opportunity to legally drop the license. Kirk said the experience of producing One Piece "ruined the company's reputation". Since then, 4Kids established a stricter set of guidelines, checks, and balances to determine which anime the company acquires.

When did one piece air on cartoon network? Let's have some stream of consciousness first.
To answer this question, we should know that: It premiered in the United States on September 18, 2004, in first-run syndication on the Fox network as part of the weekend programming block Fox Box, and later aired on Cartoon Network on their weekday afternoon programming block Toonami in April 2005. So, the answer is April 2005.