Abstract: The experiment was to investigate the changing rules of the content of amino acid and fatty acid of yak from Gannan in different ages.60 yaks in six different age- brackets were selected randomly,and fatty acid and amino acid of yak's meat were determined.The test results showed: the saturated fatty acid was the main part of fatty acid of yak's meat,and along with the growth of the age it's content had significant rose( p < 0.05).With the increase of age the unsaturated fatty acid content had decreased. P: S in every age were around 0.1. The all of n-6∶ n-3 in > 3~4 and > 4 ~ 5 year yak 's meat were in accordance with the recommended proportion. With the increase of age,the total amino acid content had increased significantly( p < 0.05). EAA / TAA and EAA / NEAA of yak's meat,which above 3 yeas,were measured up to the pattern of the FAO / WHO standard.Comprehensively,the amino acid construction and fatty acid construction of > 3~4 year yak's meat were more reasonable,and more suitable for slaughter processing.In short,there were significant effect on the content of amino acid and fatty acid of yak in different ages.Age was one of the important factors about measuring the nutrition and grading of yak.