Background: The objective of the study is to investigate the effects of reallocating time spent engaging in sedentary behavior (SB) and physical activity on the risk of mortality. Methods: In all, 332 older adult low-income and low-education populations participated in the study. At the end of the study, 273 of the participants were alive and 59 had died. Time spent undertaking moderate to vigorous physical activity (MVPA) and SB was assessed using the international physical activity questionnaire. The Cox proportional hazards regression model was used. Results: The replacement of time spent engaging in SB with MVPA reduced the risk of mortality from all causes in the older adults, resulting in reductions in mortality risk of between 10% and 46%. Conclusion: A reduction in the risk of mortality in older adults was observed when time spent in SB was replaced with the same amount of time in MVPA for all times tested.