Anaerobic co-digestion of agri-food waste is a promising management alternative. Its implementation, however, requires evaluating the proportion in which waste should be mixed to optimize their centralized treatment. The combined treatment of strawberry extrudate and fish waste, which are widely generated in Mediterranean areas, was optimized. Strawberry extrudate and fish waste were mixed and treated at different proportions (88:12, 94:6, and 97:3, respectively; wet basis). The proportions selected for the mixture allow the different flows to be absorbed simultaneously. The highest methane production was observed for the ratio 94:6 (0.205 m(3) (STP) CH4/kg volatile solid) (VS) (STP; 0 A degrees C, 1 atm), with a methane production rate in the range of 5 A center dot 10(-3)-9 A center dot 10(-3) m(3) (STP)/kg VS A center dot d, while the highest organic loading rate was observed for the mixture at a proportion 88:12 (1.9 A +/- 0.1 kg VS/m(3) A center dot d). Biodegradability was found to be similar for the 88:12 and 94:6 proportions, with values around 90 % in VS. Nevertheless, the 97:3 ratio was not viable due to a low methane production. An inhibition phenomenon occurred at increasing loads due to the effect of some compounds contained in the fish waste such as chloride or nitrogen.