Rheumatoid arthritis (RA) may share genomic risks with certain mental disorders. This study aimed at investigating associations between parental RA and risks of mental disorders in offspring. Using the National Health Insurance Research Database (2001–2010), we conducted a matched cohort study involving two parent–child cohorts (i.e., RA-parent–child cohort and non-RA-parent–child cohort) between which risks of major mental disorders in offspring were compared. There were 23,981 parent–child pairs in the RA-parent–child cohort and 239,810 in the non-RA-parent–child cohort. Preliminary analysis demonstrated increased risks of autism spectrum disorders (ASDs) [Odds ratio (OR) 1.47; 95% confidence interval (CI) 1.05–2.07], attention-deficit/hyperactivity disorder (ADHD) [OR 1.34; (95% CI 1.17–1.54)], bipolar disorder [OR 1.41 (95% CI 1.17–1.70)], and major depressive disorder [OR 1.20 (95% CI 1.07–1.35)] associated with parental RA. Sub-group analysis further showed higher risks of the four disorders in children of mothers with RA but not those from fathers with RA. Higher risks of ASDs and ADHD were not noted in children of mothers with RA before childbirth. Maternal RA, but not paternal RA or mothers diagnosed with RA before childbirth, was associated with increased risks of multiple mental disorders in their offspring, suggesting potential contributions of maternal genetic factors to ASDs and ADHD development in offspring.