The study aim was to examine constructs of autonomy support and competence as well as the motivation continuum from the self-determination theory (SDT) as a framework for understanding physical activity (PA) motivation and behavior in breast cancer survivors. Questionnaires assessing demographics, medical factors, PA, motivation continuum, perceived autonomy support, and competence were completed by 558 breast cancer survivors. Results showed that lymphedema (X2 = 7.9, p < .01) and income (X2 = 4.6, p < .05) were associated with meeting PA guidelines. Moreover, survivors meeting PA guidelines reported more identified regulations and intrinsic motivation (p < .01), autonomy support (p < .01), and competence (p < .01). Forced entry hierarchical regression analysis showed that SDT constructs explained 20.2% (p < .01) of the PA variance. Significant independent SDT predictors included identified regulation (ß = .14, p < .05) and competence (ß = .23, p < .01), with autonomy support approaching significance (ß = .9, p = .057). SDT may be a useful model for understanding PA motivation and behavior in breast cancer survivors.