Abstract: Ten beef semitendinosus muscles from bulls of Chinese yellow cattle were used to determine fatty acids changes with beef cooked or microwave heated to different internal temperature (60 ℃, 70 ℃ or 80 ℃). The obtained results showed a great variation of the respective percentages of fatty acids in neutral lipid (NL), polar lipid (PL) or total lipid (TL). Generally, polyunsaturated fatty acids (PUFA) of NC increased, while saturated fatty acid (SFA) did not change with beef cooking, and resulted in an increasing ratio of PUFA to SFA (P/S) in NL. However, in PL and TL PUFA content decreased and SFA content increased after beef cooking, which resulted in decreasing P/S ratio. But SFA increased with beef microwave heating in NL, PL and TL. Meanwhile PUFA also decreased in NL and TL, but not significantly decreased in PL. These changes resulted in P/S decreased in NL, PL and TL with beef microwave heating. M/S ratios unchanged with two heating treatments in NL, PL and TL. Value of n-6/n-3 PUFA increased significantly when beef internal temperature reached 80 ℃ in comparison with 60 ℃ or 70 ℃ despite of either cooking or microwave heating. Results suggested that beef with texture as morble should be treated with cooking but not microwave heating since P/S increased with cooking in NL and conjugated linoleic acid (CLA) also reduced significantly in NL, PL and TL. Besides, beef should not be overcooked (80 ℃) since n-6/n-3, IA (index of atherogenicity) and IT (index of thrombogenicity) increased significantly at the internal high temperature (80 ℃), which caused great changes of fatty acids and was not beneficial for human health.