Physical inactivity may an important outcome in the prognosis of breast cancer. Physical activity levelsdecrease significantly for breast cancer patients following the treatment and remain low after oncology treatmentis completed. The aim of this study was to determine physical activity levels and to examine associations amongphysical activity, comorbidity, functional capacity, peripheral muscle strength, and psychosocial status inbreast cancer patients. Forty breast cancer survivors were included in this study. Demographic and clinicalcharacteristics were recorded. Physical activity was assessed with a short form of the International PhysicalActivity Questionnaire (IPAQ). We defined comorbid diseases according to the Charlson Comorbidity Index(CCI). Functional capacity was evaluated with a six-minute walk test (6MWT). Peripheral muscle strength wasmeasured for quadriceps femoris muscle with a hand-held dynamometer. Psychosocial status was measuredwith the Hospital Anxiety Depression Scale (HADS). Forty percent of patients were inactive. The IPAQ totalscore was significantly related with quadriceps muscle strength (r=0.492; p<0.001) and HADS depression score(r=0.341; p<0.05). Marked correlations were also observed between IPAQ walking score and quadriceps musclestrength (r=0.449; p<0.001), HADS depression score (r=0.341; p<0.05), and CCI (r=-0.433; p<0.001). The CCIscore was also markedly associated with quadriceps muscle strength (r=-0.413; p<0.001). 6MWT distance wasnot significantly correlated with any of the parameters. Regression analyses revealed that psychosocial statusand peripheral muscle strength were significant predictors of physical activity estimated with the IPAQ shortform and when combined, they explained 35% of the variance. Comorbidities, peripheral muscle strength andpsychosocial status partially explain the variability of physical activity level in breast cancer survivors. Theseresults suggest that physical inactivity contributes to worsening health in breast cancer survivors.