Physical activity in early midlife has important implications for women's health. The present cross-sectional study investigated the relation of purposiveness to leisure-time physical activity, as mediated by health investment, in a sample of women in early midlife. Participants were 211 women between the ages of 35 and 45 years (mean 40.55 years, SD = 3.11) who responded to the second wave of the study of Midlife Development in the United States. Participants were originally selected by means of a nationally representative random-digit-dialing procedure. A structural equation analysis of data with latent variables was conducted with MPLUS. Purposiveness was indexed by measures of purpose in life, personal growth, and future planning. Health investment was indexed by thought and effort committed to health and the extent to which individuals worked hard to stay healthy. Leisure-time physical activity was indexed by both moderate and vigorous leisure-time activity. Results, controlling for sociodemographic factors, showed that purposiveness was associated with more physical activity and that the relation between purposiveness and leisure-time physical activity was fully mediated by health investment. These results suggest that women with a sense of purpose may be better able to achieve acceptable levels of physical activity.