Abstract：This study explored the effects of functional fitness among middle-aged and older adults using an Exercise application (APP) for Seniors. Ninety-four middle-aged and older participants were recruited in Taipei City. All subjects were asked to exercise regularly for 8 weeks with Exercise APP for Seniors. The average duration of app-use of individuals was recorded by a cloud server, and participants' improvement in functional fitness was assessed after the 8-week intervention. The results indicated that the participants aged below 65 spent most of their time watching stretching videos. Those aged above 65 primarily preferred watching videos covering comprehensive topics. The functional fitness test results reveal significant improvements among those below 65 in the chair sit and reach test, chair-stand test, 2-min step test, and 8-foot up-and-go test. However, the specific types of videos viewed were not correlated to the type of functional fitness improvements of the younger group. Although a significant improvement in functional fitness was found in both age groups, results were better for the older group. We conclude that: (1) Elderly people have different preferences regarding the usage of the Exercise APP for Seniors. (2) Significant improvements in functional fitness were also found in all of the measures except the back-scratch test among those aged 65 and above. (3) The same age group also demonstrated a significant positive correlation between performance on the single-foot standing test with eyes open and the use of muscle strength videos. (Full text)