Objective: Three types of leisure activities such as sedentary, social, and leisure-time physical activity (LTPA) have been identified as essential factors that influence mental health outcomes among older adults with diabetes. In this study, we aimed to investigate what types of leisure activities are associated with mental health outcomes among older adults with diabetes during the COVID-19 pandemic. Methods: We used 2020 Health and Retirement Study (HRS) data. We extracted 310 records from 3266 individuals diagnosed with diabetes and conducted a hierarchical regression analysis to investigate the research question. Results: LTPA was the strongest predictor of reduced loneliness and stress and increased happiness and life satisfaction among older adults with diabetes. Discussion: Our findings highlight the relationship between different types of leisure activities and mental health for older adults with diabetes during the COVID-19 pandemic. Data suggest that LTPA, social leisure, and sedentary leisure reduce loneliness and stress and improve happiness and life satisfaction.