Objective: To compare the effects of behavioral interventions targeting decreased sedentary behavior versus increased moderate-to-vigorous intensity physical activity (MVPA) in older adults. Method: Inactive older adults (N = 38, 68 ± 7 years old, 71% female) were randomized to 12-week interventions targeting decreased sedentary behavior (Sit Less) or increased MVPA (Get Active). The SenseWear armband was used to objectively assess activity in real time. Assessments included a blinded armband, the Community Health Activites Model Program for Senior (CHAMPS) questionnaire, 400-meter walk, and the Short Physical Performance Battery (SPPB). Results: Objectively measured MVPA increased in Get Active (75 ± 22 min/week, p < .001); self-reported MVPA increased in both groups (p < .05). Sedentary behavior did not change in either group (all p > .05). Only the Sit Less group improved the SPPB score (0.5 ± 0.3, p = .046). Discussion: Targeting reduced sedentary behavior had a greater effect on physical function among inactive but high functioning older adults over 12 weeks. Future studies of longer duration and combining increased MVPA with reduced sedentary behavior are needed.