Objective To solve the problem on the lower content of triglyceride ester type unsaturated fatty acids in fish oil products detected by the rapid transesterification method in the current national standard. Methods The method was improved: after dissolving samples into n-hexane, the fatty acid was then methylated with potassium hydroxide–methanol transesterification; the transesterified solution was washing to neutral with water and then detected by gas chromatography. Results The results of four main unsaturated fatty acids (?-linolenic acid, EPA, DPA and DHA) were in the satisfactory range. Conclusion The improved method was simple, accurate and reliable for the determination of triglyceride ester type unsaturated fatty acids in fish oil products.