The present invention has an object to provide a method of determining fatty acid composition in intramuscular fat on the basis of bovine genotype, in particular a method of simply determining an amount of an oleic acid content with a high degree of accuracy, and a method of objectively determining the goodness of eating quality of beef on the basis of the results of the determination. The present invention provides a method of determining an amount of fatty acid content in bovine intramuscular fat on the basis of the genotype of fatty acid synthase determined by determining base <1> and/or base <2> described below, and a method of determining whether cattles are those from which beef with an excellent eating quality is obtained on the basis of the results thereof. <1> A 16,024th base corresponding to a polymorphic site which is either adenine (A) or guanine (G) in a base sequence represented by SEQ ID NO. 1 of a sequence list. <2> A 16,039th base corresponding to a polymorphic site which is either thymine (T) or cytosine (C) in the same base sequence.