Objectives This study aimed to determine the effect of perceived exercise benefits and barriers on exercise levels among women who have been treated for breast cancer, and who were not part of formal exercise interventions. Design Anonymous, national online cross-sectional survey. Methods 432 women treated for breast cancer completed an online survey covering their treatment and demographic background, current exercise levels, and perceived exercise benefits and barriers. Each perceived benefit and barrier was considered in a binary logistic regression against reported exercise levels to ascertain significant relationships (p < 0.05) and associative values (odds ratio). Results Agreement with sixteen out of 19 exercise barriers, were significantly related to being more likely to report insufficient exercise levels, whereas agreement with 6 out of 15 exercise benefits were significantly related to being less likely to report insufficient levels of exercise. Feeling too weak, lacking self-discipline and not being a priority were the barriers with the largest association to insufficient exercise levels (OR (95% CI) = 10.97 (3.90-30.86); 8.12 (4.73-13.93); and 7.43 (3.72-14.83), respectively). Conversely, exercise enjoyment, improved feelings of well-being, and decreased feelings of stress and tension were the top three benefits associated with being less likely to have insufficient exercise levels (OR (95% CI) = (0.21 0.11-0.39), 0.21 (0.07-0.63), and 0.31 (0.15-0.63), respectively). Limitations Self-reported data measures were used to collect exercise data. Conclusions Targeting exercise barriers specific to women treated for breast cancer may improve exercise participation levels in this cohort. Awareness of the impact of exercise barriers identified in the present study will enable physical therapists to better plan exercise interventions that support all women treated for breast cancer.