Aitor Osa began his career in 1995 with the Basque Euskadi team. After two years he moved to Banesto; In 1998, he finished in the popular Spanish race Subida al Naranco place there. There he could retract his first professional victory in 2001, when he won the fourth stage of the Tour of Portugal. The following year he won a stage of the Tour of the Basque Country and secured the overall victory. Also at the Vuelta a La Rioja and again at the Portugal tour he was successful on a daily sections. A year later, he was second at the Flèche Wallonne. In 2004 he took part in the one-time Tour de France and finished it on the 50th place overall. In 2006 he ended his cycling career.
Aitor is the older brother of Unai Osa, with which he drove for a long time on the same team.
- Basque country - tour including a stage