Abstract：Lifestyle plays a crucial role in the decline of physical function. Daily activity time is a finite and physical activity (PA) that has varied health effects. However, the potential benefits of replacing sedentary time (ST) with light PA (LPA) or moderate-to-vigorous PA (MVPA) for older adults' physical function are poorly understood. Therefore, this study aims to examine the effects of replacing 10, 30, or 60-min of ST with LPA or MVPA on physical function indicators in older adults. A total of 204 adults from Taipei City, Taiwan aged ≥ 65 years were recruited. ST, LPA, and MVPA were objectively measured for seven days using triaxial accelerometers. Physical function was assessed through handgrip strength, 3-m timed-up-and-go, 6-m walking speed, and 5-time sit-to-stand tests. Results showed that: Directly replacing 10, 30, or 60-min of ST with LPA was significantly associated with different physical function indicators, while replacing any ST duration with MVPA was associated with 6-m walking speed and 5-time sit-to-stand. In conclusion: This study revealed that the practice of replacing ST with minimal LPA was positively associated with physical function improvement in older adults, while replacing ST with LPA is more beneficial than replacing ST with MVPA. (Full text)