This study examined the feasibility and potential efficacy of a multi-faceted secondary school-based intervention among low-fit adolescent females. The Sport4Fun program was designed to promote physical activity participation, fundamental movement skill proficiency, perceived physical competence, and enjoyment of physical activity in secondary school students. The intervention consisted of three components including two practical components-weekly movement skill activities for 90 min during compulsory school sport and sports-based activities for 60 min after school (non-compulsory) for 6 months- and one theoretical component-three 15-min theory sessions completed during homeroom (or roll call) time per week. The control group participated in their regular school activities. Compared with females in the control group, those in the intervention group showed a greater increase in total weekday accelerometer counts per min (adjusted difference, 77.49; 95% CI, 8.21-132.77; p = .03; Cohen's d = 1.26). The difference in total fundamentalmovement skill components mastered favored the intervention group but was not statistically significant (adjusted difference, 1.48; 95% CI, -1.21-4.17; p = .26, Cohen's d= 0.48). Targeting fundamental movement skills may be a potentially novel and motivating way to promote activity among low-fit adolescent girls; however, challenges in recruitment and implementation warrant further investigation before adopting this approach more broadly.