INTRODUCTION: n-3 polyunsaturated fatty acids (PUFAs) are believed to be implicated in the pathogenesis of many inflammation-related diseases, including depression. METHODS: The mouse model of depression was established through chronic unpredictable mild stress (CUMS), the mice were intervened with n-3 PUFAs, and then the expression of toll-like receptor 4 (TLR4) was stimulated with lipopolysaccharides (LPS). Tail suspension test (TST), forced swimming test (FST) and sucrose preference test were performed to monitor the depression behavior of mice. Microglia activation was detected by Iba1 immunofluorescence, and neuronal injury was detected by Nissl staining. Concentrations of tumor necrosis factor (TNF)-α, Interleukin (IL)-6 and IL-1β in the hippocampus were assessed via enzyme linked immunosorbent assay (ELISA). Quantitative real time polymerase chain reaction was used to detect IL-6, IL-1β and TNF-α messenger RNA levels. Western blot was utilized for detection of TLR4 protein expression. RESULTS: CUMS significantly reduced the sucrose preference in mice, while increased the immobility time in FST and TST. Moreover, CUMS significantly aggravated microglia activation and neuronal damage in mice and increased the levels of IL-6, IL-1β and TNF-α in hippocampal tissues, however, intervention with n-3 PUFAs could improve the above effects. Further, the increased TLR4 induced by LPS partially reversed the inhibition of n-3 PUFAs on depression-like behaviors, microglial activation and inflammatory injury of hippocampal neurons. CONCLUSION: n-3 PUFAs may ameliorate depression-like behaviors via reducing hippocampal neuroinflammation in CUMS-induced mice by regulating TLR4 expression, suggesting that n-3 PUFAs may be an effective antidepressant, which provides evidence for future treatment of depression.