Physical activity during breast cancer treatment can significantly reduce treatment-related fatigue and improve quality of life. Unfortunately, the majority of women with breast cancer either do not exercise at all or exercise below recommended levels. Little is known about how to enhance physical activity among breast cancer patients. The social cognitive theory, a useful framework for the design of physical activity interventions, has not been studied among breast cancer patients. Our study purpose was to explore physical activity knowledge, attitudes, and behaviors among breast cancer patients during adjuvant therapy utilizing social cognitive theory constructs in preparation for a larger, survey study and future intervention research. Twelve breast cancer patients attended 1 of 3 focus group sessions. Focus group questions were based on the social cognitive theory constructs of self-efficacy, environment, behavioral capability, expectations, expectancies, self-control and performance, observational learning, and reinforcement. The focus group participants generally felt confident in their ability to exercise during treatment if fatigue, time management, and social networking were addressed. The majority of participants had not been given information related to exercise by their physicians during treatment. The participants felt that exercise was more beneficial than harmful during treatment, with the 2 most important benefits identified as reduced fatigue and the potential for improved survival. The use of reinforcements by participants was minimal. The participants consistently expressed the desire for education and guidance by knowledgeable staff during an exercise program. Walking was the most acceptable exercise modality. Social cognitive theory may be a useful framework for future study of exercise behavior among breast cancer patients and measurement of constructs related to this theory should be included in such studies. Future exercise intervention studies should consider the unique barriers and program preferences of breast cancer patients while focusing on self-efficacy, outcome expectations/expectancies, observational learning, and reinforcements.