1993 Unai Osa Spanish Junior Champion in the road race. In 1996, he decided the Bidasoa Itzulia and the Memorial Valenciaga and 1997, the youth classification of Grande Prémio Internacional de Torres Vedras for themselves.
1997 Osa wrote a contract with the Spanish cycling team Banesto. In 1999, he won the Classique des Alpes and the Tour de l' Avenir. At the Giro d' Italia 2001, he was third in the overall standings behind Gilberto Simoni and Abraham Olano. He then took part in 2002 for the only time in the Tour de France and finished it on the 18th Place. 2006 drove Osa in the Spanish ProTour team Liberty Seguros - Würth by Manolo Saiz.
The doping scandal Fuentes Osas name appeared on Fuentes ' list that was decrypted by the Spanish judiciary.
Unai is the younger brother of Aitor Osa. The two drove from 1997 on the same team.
- Classique des Alpes
- Tour de l' Avenir