The former Mallorca and Real Valladolid star has tied himself to the club until June 2009.
Colsa, who will work under coach Cesar Ferrando, is hoping for a successful season at the Vicente Calderon.
"I'm very happy and optimistic ahead of the new season, with a great desire to play in the first-team," said Colsa to the club's official website.
"I wanted to return to Athletico. My desire to play for the club has helped things progress quickly.
"I want to put Athletico into Europe via the InterToto and then through the league directly."
