The chemical composition of three Mexican strains of Pleurotus ostreatus (INIREB-8, CDBB-H-896 and CDBB-H-897), were determined. The mushrooms were cultivated on wheat straw in a greenhouse (22-28 degrees C temperature and 80 +/- 5% of relative humidity). Fruits bodies of P. ostreatus contained (all values are expressed in g/100 g dry wt.), protein (N x 6.25): 24.64 +/- 0.21-28.50 +/- 0.26; lipids: 1.10 +/- 0.16-1.85 +/- 0.22; mineral matter: 7.66 +/- 0.23-8.79 +/- 0.25; dietary fibre: 32.14 +/- 0.14-36.81 +/- 0.40; and available carbohydrates: 26.33 +/- 1.04-30.46 +/- 0.21. They contain vitamins (mg/100 g dry wt): riboflavin: 3.31-3.7, thiamin: 1.92-1.96, niacin: 35.98-36.56 and ascorbic acid: 28-35. The main fatty acid was linoleic (0.70-1.19 g/100 g dry wt), it was also reported a low calcium and phosphorus content. Concluding the Pleurotus ostreatus could be a source of some of the complex B vitamins, dietary fiber, protein and linoleic acid.