Objective Physical activity after a diagnosis of breast cancer is associated with many health benefits. Health literacy has been shown to relate to physical activity, but there is limited research on this relationship. The aim of this study was to explore the relationship between health literacy and physical activity in women diagnosed with breast cancer. Specifically, we examined which of Nutbeam's 3 levels of health literacy (functional, interactive, and critical health literacy) predicted physical activity in women who have completed treatment for breast cancer. Methods Participants were women (N = 36) who had attended a local cancer care centre for breast cancer treatment. During a telephone interview conducted 6 to 18 months after completion of treatment, women completed a measure of health literacy and reported on their engagement in physical activity. Results Results showed that health literacy predicted physical activity after breast cancer treatment. Of the 3 levels of health literacy proposed by Nutbeam, functional health literacy was shown to be the most important predictor of physical activity. Conclusions These findings highlight the role of health literacy in physical activity in women diagnosed with breast cancer and have implications for targeted supportive physical activity interventions.