PURPOSE: To identify distinct trajectories of physical health-related quality of life (HRQoL) in older women over the first two years following breast cancer diagnosis, and to examine characteristics associated with trajectory group membership. METHODS: A secondary analysis of a longitudinal study of women diagnosed with stage I-III breast cancer who completed surveys within eight months of diagnosis and six, twelve, and eighteen months later that focuses on a subset of women aged ≥ 65 years (N = 145).Physical HRQoL was assessed using the Physical Component Score (PCS) of the SF-36 Health Survey. Finite mixture modeling identified distinct PCS trajectories. Multivariable logistic regression identified variables predictive of low PCS group membership. RESULTS: Two distinct patterns of PCS trajectories were identified. The majority (58%) of women had PCS above the age-based SF-36 population norms and improved slightly over time. However, 42% of women had low PCS that remained low over time. In multivariable analyses, older age, difficulty paying for basics, greater number of medical comorbidities, and higher body mass index were associated with low PCS group membership. Cancer treatment and psychosocial variables were not significantly associated. CONCLUSION: A large subgroup of older women reported very low PCS that did not improve over time. Older age, obesity, multiple comorbidities, and lower socioeconomic status may be risk factors for poorer PCS in women with breast cancer. Incorporating routine comprehensive geriatric assessments that screen for these factors may help providers identify older women at risk for poorer physical HRQoL post breast cancer treatment.