BACKGROUND: The salutary effects of resistance exercise training (RET) are well established, including increased strength and function; however, less is known regarding the effects of RET on mental health outcomes. Aerobic exercise has well-documented positive effects on anxiety, but a quantitative synthesis of RET effects on anxiety is needed. OBJECTIVES: To estimate the population effect size for resistance exercise training (RET) effects on anxiety and to determine whether variables of logical, theoretical, and/or prior empirical relation to anxiety moderate the overall effect. METHODS: Thirty-one effects were derived from 16 articles published before February 2017, located using Google Scholar, MEDLINE, PsycINFO, PubMed, and Web of Science. Trials involved 922 participants (mean age = 43 ± 21 years, 68% female/32% male) and included both randomization to RET (n = 486) or a non-active control condition (n = 436), and a validated anxiety outcome measured at baseline, mid-, and/or post-intervention. Hedges' d effect sizes were computed and random effects models were used for all analyses. Meta-regression quantified the extent to which participant and trial characteristics moderated the mean effect. RESULTS: RET significantly reduced anxiety symptoms (Δ = 0.31, 95% CI 0.17-0.44; z = 4.43; p < 0.001). Significant heterogeneity was not indicated (Q (T)(30) = 40.5, p > 0.09; I (2) = 28.3%, 95% CI 10.17-42.81); sampling error accounted for 77.7% of observed variance. Larger effects were found among healthy participants (Δ = 0.50, 95% CI 0.22-0.78) compared to participants with a physical or mental illness (Δ = 0.19, 95% CI 0.06-0.31, z = 2.16, p < 0.04). Effect sizes did not significantly vary according to sex (β = -0.31), age (β = -0.10), control condition (β = 0.08), program length (β = 0.07), session duration (β = 0.08), frequency (β = -0.10), intensity (β = -0.18), anxiety recall time frame (β = 0.21), or whether strength significantly improved (β = 0.19) (all p ≥ 0.06). CONCLUSIONS: RET significantly improves anxiety symptoms among both healthy participants and participants with a physical or mental illness. Improvements were not moderated by sex, or based on features of RET. Future trials should compare RET to other empirically-supported therapies for anxiety.