Self-reported altruistic activity and social capital were examined as predictors of perceived happiness and life satisfaction among a sample of 4,486 Canadians aged 65 or more years from the 2003 Canadian General Social Services Survey, Cycle 17. Altruistic behaviour was measured by number of volunteer hours per month and helping others (not including family and friends). Social capital was measured using dimensions of belonging to one's community, community and neighbour trust, and group activities. Drawing on generativity and role-identity theories, it was hypothesised that altruistic behaviour and social capital are positively associated with well-being (using perceived happiness and life satisfaction), and that social capital mediates the relationship. For both perceived happiness and life satisfaction, after controlling for demographic, health status, and social support variables, measures of altruistic behaviour demonstrated statistically significant associations. Once measures of social capital were entered into the analysis in the final block, however, the altruistic behaviour variables were no longer statistically significant. Robust associations were found for social capital and the two measures of well-being, particularly between sense of belonging, trust in neighbours, and perceived happiness and life satisfaction. The findings suggest that altruistic behaviour is mediated by social capital. The implications of these findings are discussed with respect to understanding the well-being of older Canadians.