For the conduction of this work, 24 males from four different genetic groups (5/8 Charolais (CH) 3/8 Nellore (NE); 5/8 NE 3/8CH; 3/4 CH 1/4NE e 3/4NE 1/4CH) and two ages: steers and young steers were used. The animals received a diet composed of corn silage and concentrate with roughage:concentrate ratio of 50:50. After slaughter, the carcasses were identified and chilled. A steak from the longissimus muscle was collected and dried in stove, grounded, identified and stored for lipid extraction. The fatty acids (FA) determination was performed through gas chromatograph. No significant interaction was observed between category and genetic groups and marbling, fat thickness, muscle:fat ratio, used as co-variables. The total trans18 FA was higher (2.46%) for young steers in relation to steers (1.87%). Most short-chain (75%) and medium-chain (91.7%) FA were not influenced by the genetic group. CLA values did not differ between CH-NE crossbred animals. Animals with NE predominance showed higher saturated FA (average of 54.7%) in relation to CH animals (average of 49.5%). In relation to the unsaturated/saturated ratio, higher value was observed for CH animals.