Objectives: Studies indicate women aged 25-49 years previously treated for cancer report cognitive alterations. Good evidence indicates physical activity can be beneficial after cancer and might additionally benefit cognitive function. This short report presents data from a substudy of the Younger Women's Wellness after Cancer Program (YWWACP), which explored cognitive alterations and investigated potential associations between physical activity and cognitive function in participants in the YWWACP. The primary aim of this substudy was to determine in younger women previously treated for breast cancer (1) whether subjectively reported cognitive function changed over time and (2) if physical activity is associated with subjectively reported cognitive function, and if time had an impact on this. Methods: All participants had completed breast cancer treatment. Data were collected at baseline (n=41) and at 12 weeks. Measures assessed demographics, self-reported physical activity, cognitive function, sleep quality, stress, anxiety and depression using validated and reliable, subjectively reported instruments. Results: Cognitive function and physical activity scores increased across the time points, with cognitive function revealing a statistically significant increase over time (p=0.004). Statistical testing revealed that physical activity was not correlated with cognitive function and that change in physical activity was not correlated with change in cognitive function. Conclusion: These data provide early evidence that cognitive function and physical activity improved over time in this sample. However, interpretations of a correlation between physical activity and cognitive function should be made with caution, and future research would benefit from larger samples.