The favorable role of n-3 polyunsaturated fatty acid (PUFA) in cardiovascular disease (CVD) has been demonstrated in animal experiments and in humans in Western countries, but its effect remains controversial in Asian populations. An observational study of Japanese, Koreans and Mongolians with extended histories of remarkably different frequencies of fish intake was conducted to examine whether differences in plasma n-3 PUFA affects CVD risk factors. We conducted a cross-sectional study in workplace settings and determined body mass index (BMI), blood pressure, total cholesterol, LDL-cholesterol, HDL-cholesterol, triglyceride (TG), glucose, insulin, homeostasis model assessment-insulin resistance (HOMA-IR) and fatty acid composition in plasma. A total of 411 Japanese, 418 Korean and 252 Mongolian workers aged 30-60 yr participated in this study. The Japanese ate fish more frequently and had remarkably higher values of eicosapentaenoic acid, docosahexaenoic acid and n-3 PUFA, and lower values of BMI and HOMA-IR, followed by the Koreans, and then the Mongolians. In age groups, the Japanese and Koreans showed a similar tendency of increase in n-3 PUFA with increasing age. General linear measurement multivariate analysis after adjustment for gender, age, smoking, drinking, exercise habits and BMI showed n-3 PUFA was associated with HDL-C and TG in the Japanese, while it was associated with systolic blood pressure in the Koreans, and TG in the Mongolians. In conclusion, an increase in n-3 PUFA was associated with HDL-C and TG in the Japanese and Mongolians, but these beneficial effects were not constant across the three Asian ethnic groups.