The purpose of this study is to explore the relationship between physical activity and working memory decline among older adults with APOE4 status. The APOE4 allele is currently the strongest predictor of risk for Alzheimer's disease and other related dementias. The publicly available data from the Health and Retirement Study was used to complete this Retrospective Longitudinal study. Three hypotheses were explored. H₁: It is expected that the presence of the APOE4 allele will be associated with worse overall working memory performance and a steeper rate of decline in working memory over time. H₂: Meanwhile, it is expected that participants that partake in a higher physical activity level will have better overall working memory performance and less decline in working memory than participants that only perform low or no activity. H₃: A moderation effect of physical activity on the relationship between working memory and APOE4 status is expected. A two-way repeated measure ANOVA was performed. Results indicted main effects for physical activity and years of education on the digit span task. Additionally, it was found that vigorous activity mitigates ill-effects of APOE4 on working memory. A statistical significance was found for the interaction between APOE4 status and physical activity. Findings suggest that physical activity may be prioritized as a primary intervention method for older and middle-aged APOE4 carriers.