The Meaningful Activity Participation Assessment (MAPA), a recently developed 28-item tool designed to measure the meaningfulness of activity, was tested in a sample of 154 older adults. The MAPA evidenced a sufficient level of internal consistency and test-retest reliability and correlated as theoretically predicted with the Life Satisfaction Index-Z, the Satisfaction with Life Scale, the Engagement in Meaningful Activities Survey, the Purpose in Life Test, the Center for Epidemiologic Studies Depression Inventory and the Rand SF-36v2 Health Survey subscales. Zero-order correlations consistently demonstrated meaningful relationships between the MAPA and scales of psychosocial well-being and health-related quality of life. Results from multiple regression analyses further substantiated these findings, as greater meaningful activity participation was associated with better psychological well-being and health-related quality of life. The MAPA appears to be a reliable and valid measure of meaningful activity, incorporating both subjective and objective indicators of activity engagement. (Contains 7 tables.)