The objective was to assess interactive effects of methylmercury (MeHg) and n‐3 long‐chain polyunsaturated fatty acids (LCPUFA) on brain essential fatty acids in animals exposed chronically to MeHg and fed a diet with (+) or (‐) without n‐3 LCPUFA. Female rats (n=8/grp) were exposed for 1 yr to 0, 0.5, & 5 ppm MeHg in water and consumed a diet containing palm, safflower, soybean and either coconut in (‐) n‐3 diet or fish oil in (+) n‐3 diet. Fatty acids of the phosphatidylcholine (PC) and phosphatidyl‐ethanolamine (PE) fractions of the adult rat brain were determined by gas capillary chromatography. In the adult forebrain, chronic MeHg exposure had no significant effects on the alteration of the major LCPUFA; docosahexaenoic acid (DHA) and arachidonic acid (ARA), as well as total n‐3 and total n‐6 fatty acids. However, there was a dietary effect showing a significant increase in DHA in both the PE (23‐30% increase) and PC (25‐46% increase) fractions in animals consuming dietary fish oil compared with those consuming the coconut oil diet (P<0.001). There were significant decreases of ARA in both the PE (18‐20% decrease) and PC (12‐28% decrease) fractions. Thus, fatty acids in the adult rat brain can be influenced by long‐term feeding of dietary fish oil, but chronic mercury exposure had no effect on brain LCPUFA. (Funded by AAES 13‐014)