The aim of this study was to evaluate the inclusion of extruded red lentil meal as a plant protein source in a rainbow trout diet. Rainbow trout (n = 207) were randomly allocated to the control and two treatment groups. Diets were isonitrogenous and isocaloric. The control diet contained no extruded red lentil meal. Fish in treatments 1 and 2 were fed diets containing 10% and 15% extruded red lentil meal, respectively. Fish were fed twice a day to apparent satiation for 84 days. There were no significant (p>0.05) differences in weight gain, feed conversion ratio, protein efficiency ratio, dorsal muscle composition, or survival. Digestibility of nitrogen free extract+crude fiber was higher in the experimental groups than in the control. Thus, extruded red lentil meal can be considered as a protein source for rainbow trout diets up to the level of 15%.