We examined the mediating role of optimism in the relationship between mindfulness and positive affect with a sample of 277 Chinese people aged between 51 and 65 years who completed the Mindful Attention Awareness Scale, the Life Orientation Test-Revised, and the Positive Affect subscale of the Positive and Negative Affect Schedule. Pearson correlation analysis results showed a significant positive relationship between mindfulness, optimism, and positive affect. Mediation analysis results further showed that optimism partially mediated the association between mindfulness and positive affect. Thus, as the findings indicated that enhancing mindfulness levels results in greater optimism, this should be considered an effective measure for promoting positive affect in older adults.