Heifers of Limousine (LI) and Charolais (CH) breed were used to evaluate the effect of a basal mixed diet with linseed supplementation (108 g.kg-1 DM) on performance and fatty acid (FA) composition of M. longissimus thoracis (MLT) and subcutaneous fat. In summary, both diet and genotype influenced the FA profile of MLT. Live weight gains were higher in the CH heifers compared with the LI heifers, but did not differ between diets within the breed. Feeding linseed enhanced the nutritive value of beef in terms of FA profile. The lipids of the LI heifers contained more FAs that are considered important for human health.