The aims of the present study were to compare the quality of grain-fed and pasture-fed beef and to assess the effects of two feeding periods on grain for finishing steers. A group of 75 steers were fed one of 5 finishing diets (n = 15 per diet): pasture for 90 d (P), oat grain plus pasture silage for 35 d (SO), oat grain plus pasture silage for 75 d (LO), wheat grain plus pasture silage for 35 d (SW), and wheat grain plus pasture silage for 75 d (LW). The physicochemical and sensory attributes and the fatty acid composition of the longissimus lumborum muscle were determined. The beef from pasture-fed animals tended to be tenderer, darker, less red, and with yellower fat than the beef from grain-fed steers. The beef from steers fed wheat plus silage for 75 d had lower tenderness scores than beef from steers fed for 35 d on grain plus silage. The beef from pasture-fed steers had higher levels of conjugated linoleic acid c-9 t-11 and n-3 fatty acids and a lower n-6:n-3 fatty acid ratio than the beef from grain-fed steers. The time fed on grain plus silage had a significant effect on the fatty acid composition of the beef from steers fed wheat, but no similar effect was observed in beef from steers fed oats. However, the n-6:n-3 ratio of beef was more favorable when steers were fed grain (wheat or oats) plus silage for 35 d than for 75 d.