Essential fatty acids could regulate inflammation, especially n-3 PUFA (n-3 polyunsaturated fatty acids), which are considered to have a protective effect to inhibit neuroinflammation. Peony seed oil is one of the most abundant n-3 PUFAs in oils. but the mechanism of peony seed oil affecting inflammation in mice brains is still lacking convincing evidence. Sixty male C57BL/6J mice were randomly allocated into four groups: D-gal (D-galactose) induced model group, FO (D-gal + fish oil), PSO (D-gal + peony seed oil). After 10 weeks, the fatty acid composition in liver and brain tissues and potentially related genes were examined. Docosahexaenoic acid (DHA) was significantly higher, while arachidonic acid (AA) was significantly lower in both in the PSO and FO groups than that in the model group in the brain and liver. In the PSO and FO groups, the relative mRNA levels of