Abstract: The topic about the source and quality of fresh milk is an international research. The fatty acids content and the carbon isotope ratio were analyzed to record the difference between convention and organic milk. The results show that these indicators of convention milk researched are no obvious difference. But that of convention and organic milk have notable differences， organic milk contained more polyunsaturated fatty acids than convention milk, especially in linolenic acid and conjugated linoleic acid. The content of linolenic acid in convention milk is about 0.15%, while organic milk has a higher content (at lease δ¹³C values are found in organic milk.