To investigate the effects of dietary fatty acids on liver and serum lipid as well as on erythrocyte membrane, 23%(w/w) lard (as saturated fatty acids SFA), 23%(w/w) corn oil (as polyunsaturated fatty acids PUFA) and 5%(w/w) corn oil (as low fatty acids LFA control) were fed respectively to three groups of Wistar rats for 35 and 63 days. The study showed that the pattern of liver fatty acids was correlated with that of dietary fatty acids. Serum VLDL-Ch was lowered in PUFA group when compared with that in SFA group. The osmotic fragility and hemolytic rate of RBC were elevated in PUFA group, but lowered in SFA group. The membrane fluidity of RBC in PUFA group tended to increase. The immune adhesive activity of RBC C3b receptor was impaired when high dietary fat (PUFA, SFA) were given to rats. This study indicates that high dietary fatty acids have adverse effect on RBC membrane structure and immune adhesive function. That high PUFA is good for health is not always correct.