Past studies have established the link between retirement planning and mental health in the workplace, yet the possible effect of self-efficacy in this association has not been explored in the extant literature. This study investigates the mediating impact of self-efficacy in the link between retirement planning and mental health among workers in Ilorin, Nigeria. A sample of 243 (M = 55.1%; Mean age = 58.02, SD = 3.16) older workers responded to three scales viz: Mental Health Scale (MHS), Retirement Planning Scale (RPS), and Self-Efficacy Scale (SSS). Data were performed with the Pearson Product Moment Correlation (PPMC) and Hayes PROCESS macro statistical tools. The result shows that retirement planning positively predicted mental health. Also, mental health positively predicted self efficacy while self efficacy also positively predicted mental health. The mediation analysis revealed that self efficacy had a partial mediation on the association between retirement anxiety and mental health. The study concludes that retirement planning can only be sustained when workers inculcate a high self efficacy which in turn may improve their mental health. The study recommended that intervention programmes tailored toward improving the self efficacy of older workers which would improve their retirement planning should be implemented as this will enhance their mental health.