Limited physical activity, sedentary behavior, and reduction in muscle mass, strength, and function are accompanied by negative outcomes. The relationship between these factors and physical and mental health-related quality of life (HRQoL) has yet to be elucidated in continuing care retirement community (CCRC) residents. The current study investigated the relationships among physical activity, sedentary behavior, and muscle mass, strength, and function to physical and mental HRQoL. A sample of 105 CCRC residents participated in this cross-sectional correlational study. Findings demonstrated that low physical activity and muscle function were significantly associated with low physical HRQoL and explained 38% of the variance in physical HRQoL. Handgrip strength was significantly associated with low mental HRQoL and explained 8% of the variance in mental HRQoL. Older adults living in CCRCs may benefit from interventions targeting physical activity and the distinct muscle components of sarcopenia that have the potential to improve physical and mental HRQoL. [Research in Gerontological Nursing, 15(3), 131-139.].