The Basque giants have confirmed their second signing for the new season as the experienced striker has decided to return to San Mames after a short stint at Mestalla
The 31-year-old, who has one international cap to his name, has signed a three-year contract with the Basque side which will keep him at San Mames until 2015.
The transfer feel has not been revealed by either club, but reports suggest that Aduriz has cost Athletic a fee in the region of €2.5 million.
He joined Valencia from Mallorca in 2010 in a €4m deal but failed to impress at Mestalla, scoring 21 goals in 82 appearances for Los Che.
The Spanish striker will now return to Athletic for a third spell after previously playing for the club in 2002-03 and again between 2006 and 2008.