Background: Frail or prefrail older adults have risks of falling, disability, hospitalization, and death. The effects of a fitness training program conducted in the community is unknown. The aims of this study were to investigate the effects of a 12-week community-based fitness program on functional fitness and weight in frail and prefrail older adults. Methods: A quasi-experimental design was conducted and older adults who met the frail or perfrail criteria were recruited. The participants were assigned to the intervention or control groups based the communities. The intervention group (n=49) received 2 hours of multiple components fitness training once a week for 12 consecutive weeks and the control group (n=26) maintained routine activities. Functional fitness tests including upper and lower body strength, upper and lower body flexibility, alternative aerobic test, dynamic balance/agility and static balance; and weight, body mass index (BMI), and waist circumstance were collected before and after the fitness training program. Results: After 12 weeks, compared with the control group, the intervention group had significant increases in weight (F=9.58, p=0.002) and BMI (F=6.03, p=0.004), but no improvement in functional fitness. Conclusions: The 12-week fitness training program included multiple components is effective for weight and BMI in frail and prefrail older adults in communities, but it needs more training for functional fitness.