[Eighteen cows were fed, for 8 weeks, 3 isonitrogenous and isoenergetic unifeed diets differing in soybean type supplementation: meal (FES), chopped toasted (TS) and extruded (SE). The amount of administered soybean ranged from 2.10 to 2.45 kg/head/d. Milk yield, protein, fat, urea content and renneting properties were not significantly different in the three groups. The saturated/unsaturated fatty acid ratio decreased from ES to TS and SBM (2.48, 2.17 and 1.93, respectively), while the CLA content increased (0.557, 0.617 and 0.908% of total fatty acids, respectively for FES, ST and SE). Rumen parameters and main metabolism indicators were similar among groups. In conclusion, the addition of toasted soybean and, especially, extruded soybean in replacement to meal can improve the milk fatty acid profile and increase, particularly, the CLA content.]