Little is known about how different lifestyle factors mediate the relationship between socioeconomic status (SES) and health among middle-aged and older adults in Korea. Using data from the Korean Longitudinal Study of Aging, this study examined the direct effects of SES on self-rated health and how lifestyle factors mediate the relationships between SES and self-rated health. This study further tested whether the effects of SES and lifestyle factors differ as people age. The findings indicate that higher levels of income and education as well as not being in poverty predicted better self-rated health. Meanwhile, engaging in regular exercise and being underweight significantly mediated the relationship between education and self-rated health as well as between poverty and self-rated health. Finally, poverty and regular exercise had a greater impact on self-rated health in old age than in middle age. Implications for enhancing antipoverty policies and exercise programs are discussed.