BACKGROUND: Unsaturated fatty acids might be involved in the prevention and improvement of mental disorders, but the evidence on these associations has not been comprehensively assessed. OBJECTIVE: This umbrella review aimed to appraise the credibility of published evidence evaluating the associations between unsaturated fatty acids and mental disorders. METHODS: In this umbrella review, systematic reviews and meta-analyses of studies comparing unsaturated fatty acids (including supplementation, dietary intake and blood levels) in participants with mental disorders versus healthy individuals were included. We reanalyzed summary estimates, between-study heterogeneity, predictive intervals, publication bias, small-study effects, and excess significance bias for each meta-analysis. RESULTS: Ninety-five meta-analyses from 29 systematic reviews were included, encompassing 43 studies on supplementation interventions, 32 studies on dietary factors and 20 studies on blood biomarkers. Suggestive evidence was only observed for dietary intake, in which higher intake of fish was associated with reduced risk of depression (relative risk [RR]: 0.78; 95% CI: 0.69, 0.89) and Alzheimer's disease (RR: 0.74; 95% CI: 0.63, 0.87), and higher intake of total polyunsaturated fatty acids (PUFAs) might be associated with a lower risk of mild cognitive impairment (RR: 0.71; 95% CI: 0.61, 0.84). Evidence showed that PUFA supplementation was favorable but had weak credibility in anxiety, depression, attention-deficit/hyperactivity disorder (ADHD), autism spectrum disorder (ASD), dementia, mild cognitive impairment, Huntington's disease and schizophrenia (P random-effects: <0.001-0.040). There was also weak evidence on decreased circulating n-3 PUFAs among patients on risk of ADHD, ASD, bipolar disorder, and schizophrenia (P random-effects: <10-6-0.037). CONCLUSIONS: Our results suggest that higher levels of unsaturated fatty acids may relieve symptoms or reduce the risk of various mental disorders; however, the strength of the associations and credibility of the evidence were generally weak. Future high-quality research is needed to identify whether PUFA interventions should be prioritized to alleviate mental disorders.