The change in fatty acid composition in brain tissue of the second generation rats(Sprague-Dawley strain) was studied using four different fat diets(Corn oil=CO, Soybean oil=SO, Perilla oil=PO, Fish oil=FO, 10% by Wt). The experimental diets were started from pregnancy in four different groups, each consisting of 9 rats. The seound generation rats were fed the same diet as their mothers. Animals were anesthetized with ether at 0, 3, 9 & 16 weeks of age. Whole brains were dissected out, brain tissues were, then, homogenized and lipids were extracted from brain tissues. The fatty acid compositions were measured after methylation by gas-liquid chromatography at 0, 3, 9 and 16 weeks of age of offspring. The changes in the relative concentrations of polyunsaturated fatty acids(PUFA) or more specifically docosahexaenoic acid(22 : 6, $omega$3, DHA), the major $omega$3 fatty acid component in rat brain at different age were similar to changes in the amount of DNA in brain tissue showing the maximum value during the lactation. The changes in saturated fatty acid(SFA) content showed a contrasting patten to those of PUFA, while monounsaturated fatty acid(MUFA) increased steadily throughout the experimental period. At birth, the relative concentrations of $omega$3 series fatty acids the relative concentrations of PUFA, MUFA and SFA converged to very similar values respectively regardless of the dietary fatty acid compositions. In brain tissue, it is of value to note that while changes in relative concentrations of linoleic acid (18 : 2, $omega$6, LA) and arachidonic acid(20 : 4, $omega$6, AA) showed a precursor-product-like relationship, $alpha$-linolenic acid(18 : 3, $omega$3, $alpha$-LnA) and DHA showed a different pattern. Even when the $omega$3 fatty acid content in very low in maternal diet(CO), the second generation rat brain tissues appeared to secure DHA content, suggesting an essential role of this fatty acid in the brain. The fact that a large amount of $alpha$-LnA in the maternal diet did not have a significant effect on the second generation rat brain $alpha$-LnA content, indicated that DHA seemed essential component for the brain development in our experimental condition. In all groups, the relative content of $alpha$-LnA in the brain tissues remained relatively constant throughout the experimental period at the very low level. The study of the specific concentrations and essential role(s) of DHA in each parts of brain tissue is needed in more details.