UNLABELLED: While moderate- to vigorous-intensity physical activities (MVPA) confer the greatest health benefits, evidence suggests that light-intensity activities are also beneficial, particularly for older adults and individuals with moderate to severe comorbidities. PURPOSE: To examine cross-sectional and longitudinal associations between light-intensity activity and physical function in older cancer survivors at increased risk for age- and treatment-related comorbidities, including accelerated functional decline. METHODS: The analysis included data from 641 breast, prostate, and colorectal cancer survivors (54% female) age 65 yr and older who participated in a 1-yr home-based diet and exercise intervention designed to reduce the rate of physical function decline. ANCOVA was used to compare means of physical function across levels of PA intensity (low-light [LLPA]: 1.5-2.0 METs; high-light [HLPA]: 2.1-2.9 METs; MVPA: ≥3.0 METs). RESULTS: In cross-sectional analyses, increasing tertiles of light-intensity activity were associated with higher scores for all three measures of physical function (all P values <0.005), after adjusting for age, sex, body mass index, comorbidity, symptoms, and MVPA. Associations were stronger for HLPA than for LLPA. Compared with survivors who had decreased MVPA or maintained stable MVPA and HLPA at the postintervention follow-up, those who had increased HLPA, but had decreased MVPA or maintained stable MVPA, reported higher physical function scores (LS means [95% confidence interval]: SF-36 Physical Function Subscale: -5.58 [-7.96 to -3.20] vs -2.54 [-5.83 to 0.75], P = 0.14; Basic Lower Extremity Function: -2.00 [-3.45 to -0.55] vs 0.28 [-1.72 to 2.28], P = 0.07; Advanced Lower Extremity Function: -2.58 [-4.00 to -1.15] vs 0.44 [-1.52 to 2.40], P = 0.01). CONCLUSIONS: Our findings suggest that increasing light-intensity activities, especially HLPA, may be a viable approach to reducing the rate of physical function decline in individuals who are unable or reluctant to initiate or maintain adequate levels of moderate-intensity activities.