A multimodal exercise training program might be the best way to improve motor and cognitive function in patients with Parkinson's disease (PD), but this has yet to be fully proven in PD patients with mild cognitive impairment (MCI). This study aims to examine the feasibility and effectiveness of a theory-based, multi-component exercise intervention in older people with PD-MCI. Participants were randomized into an intervention group (n=23) and an active control group (n=23), receiving the theory-based multi-component exercise intervention and Parkinson's health exercises, respectively. All participants performed 60-minute exercise training sessions three times a week over a 12-week period. The retention rate at post-intervention was 95.7% (42/46) for the entire cohort. The attendance rates were 99.6% in the intervention group and 99.5% in the control group. No adverse events occurred. The intervention group showed significantly greater improvements than the control group in global cognitive function, executive function, physical motor function, balance and gait, depression, and quality of life. This study indicates that the theory-based multi-component exercise intervention demonstrates high feasibility in promoting exercise adherence and is an effective treatment option for older adults with PD-MCI.