Abstract: This study was performed to determine the effects of dietary supplementation of fish oil rich in DHA during development of rats on the learning and memory ability of the young rats.A control group(O)of maternal rats were fed with fundamental diet and theiryoung rats received similar diet from weanling to the age of 45 days.Other three groups were fed with fundamental diet+fish oil(doses of DHA were 7.5(A),15(B),30(C)g/kg diet).The findings showed that learning ability of group B and C improved compared to the control group(P<0.05)and grou B was the most significant;5-HT,DA and SS contents of young rats hippocampus were higher in group A,B and C compared to the control group.Conclusion: 1.Supplementation of DHA during development could improve learning ability of young rats and the optimal dose was 15g/kg diet.2.DHA improving learning ability might related to 5-HT,DA,SS rising in hippocampus and other transmitter or other michanism.