Twenty Angus steers (278 ± 21.4 kg BW) were used to evaluate the effect of high concentrate diets during stocker and finishing phases on lipid fractions [neutral lipid (NL), phospholipid (PhL) and free fatty acid (FFA)] in longissimus muscle. Steers were randomly assigned to 2 treatments: (1) high quality forage grazed during all phases (PAST) or (2) high concentrate diets fed during early stocker (111 d) phase and finishing phase (77 d) with an intermediate period on high quality forage (98 d) between stocker and finishing periods (FPF). Steers were slaughtered at a similar live weight endpoint (568 kg BW). Longissimus muscle samples were obtained from each animal. Lipids were extracted from the LM, separated into lipid fractions (NL, PhL, and FFA) and fatty acid composition of each fraction analyzed by GLC. Feeding of high concentrates during the stocker phase and finishing phase increased (P < 0.05) total fatty acid content of the LM compared with PAST (4.96% vs. 3.38%, respectively). On a gravimetric basis, FPF had greater NL and FFA content than PAST. However on a percentage basis, the lipid fractions were similar (P > 0.05) between PAST and FPF. Overall, the LM contained 93.7% NL, 5.0% PhL, and 1.6% FFA. In the NL, FPF had greater (P < 0.05) concentrations of MUFA, n-6 PUFA, and n-6 to n-3 ratio of PUFA compared with PAST. The PAST had greater (P < 0.05) concentrations of n-3 fatty acids in NL than FPF. In the PhL, PAST had greater (P < 0.05) MUFA and n-3 PUFA compared with FPF. The PhL fraction of FPF had greater (P < 0.05) concentrations of n-6 PUFA and higher ratio of n-6 to n-3 PUFA. Fatty acid composition of FFA fraction did not differ (P > 0.05) between treatments. These results indicate that PAST finished beef has increased n-3 PUFA concentrations in the LM due to greater accumulation of n-3 PUFA in both NL and PhL fractions and not because of a greater PhL contribution to the total lipid fraction.