Argentine meat has been traditionally produced on pasture. However, to comply with some market requirements, grain finishing is becoming more common among producers. The main goal of the present work was to study lipid oxidation in fresh meat from animals fed different diets in relationship with their antioxidant vitamin status. Attributes were evaluated in beef from pasture or grain-fed animals with (PE and GE) or without supplementation (P and G) with vitamin E (500 UI/head/day). Fresh meat produced on grain (G and GE) had higher fat (4.0±1.6 and 4.7±1.4 g/100 g) and cholesterol content (51.0±3.0 and 52.0±4.0 mg/100 g) than meat from pasture (P and PE) fed animals (2.7±1.2 to 2.9±1.1 g/100 g and 48.0±5.0 to 49.0±4.0 mg/100 g of intramuscular fat and cholesterol respectively). Fatty acid composition was clearly affected by diet. Beef from pasture-fed cattle had higher percentage of linolenic acid, less linoleic acid and, overall, higher percentage of polyunsaturated fatty acids than beef from grain-fed animals (P<0.05). Thiobarbituric acid reactive substances number and volatile levels of hexanal, pentanal, heptanal, octanal and 3-methylbutanal were higher in grain than in pasture samples (P<0.05). P+PE meat had higher content of antioxidant vitamins than G+GE samples (P<0.001). Values ranged from: 15.92±3.48 (G) to 17.39±4.29 (GE) and 25.3±10.0 (P) to 21.98±5.11 (PE) μg/g of ascorbic acid; from 1.05±0.73 (G) to 1.76±0.97 (GE) and 3.08±0.45 to 3.91±0.74 μg/g of α-tocopherol; and from 0.06±0.03 (G) to 0.05±0.01 (GE) and 0.45±0.21 (P) to 0.63±0.27 (PE) μg/g of β-carotene. In addition, principal component analysis clearly separated grain from pasture samples regardless of their supplementation with vitamin E. This level of supplementation did not improve the antioxidant status of fresh meat (P>0.05). We conclude that pasture diet contributes natural antioxidants in sufficient amounts and is an efficient way to prevent lipid oxidation in fresh beef.