This eight-year follow-up study examines the roles of physical and leisure activity as predictors of mental well-being among older adults born in 1904-1923. As part of the Evergreen project, 1224 (80%) persons aged 65-84 years were interviewed at baseline (1988), and 663 (90%) persons in the follow-up (1996). Mental well-being factors including depressive symptoms, anxiety, loneliness, self-rated mental vigour and meaning in life were constructed using factor analysis. The predictors of mental well-being included physical and leisure activity, mobility status and number of chronic illnesses. We used a path analysis model to examine the predictors of mental well-being. At baseline, low number of chronic illnesses, better mobility status and leisure activity were associated with mental well-being. Baseline mental well-being, better mobility status and younger age predicted mental well-being in the follow-up. Explanatory power of the path analysis model for the mental well-being factor at baseline was 19% and 35% in the follow-up. These findings suggest that mental well-being in later life is associated with activity, better health and mobility status, which should become targets for preventive measures.