Physical activity is frequently proposed as an intervention to reduce fatigue and sleep disturbance in cancer survivors; however, the long-term effects of physical activity are often not reported, and older adults are typically excluded from these intervention studies. This article aimed to examine if postdiagnosis physical activity is associated with lower long-term fatigue and sleep disturbance in older adult breast cancer survivors. Data were analyzed of a prospective cohort of 440 breast cancer survivors aged 65 years or older from the Women’s Health Initiative study. Multiple linear and logistic regression models were used to examine associations of physical activity with fatigue and sleep disturbance. Higher postdiagnosis physical activity was associated with lower long-term fatigue but was not associated with lower sleep disturbance after adjusting for demographics, cancer characteristics, and baseline measures.