Our country has become an aged society. Thus, slowing down the decline and maintaining the physical fitness of the elderly is imperative. This study shows the impact of high-intensity rehabilitation exercise training on physical fitness and activity of daily living among frail elderly. The cases were three individuals aged 75 and above who participated in high-intensity rehabilitation exercise training conducted 2 hours per day and five days a week for three weeks. Muscle strength tests for the upper and lower limbs, lower limb flexibility tests, cardiorespiratory endurance tests, agility tests, balance ability assessments, and activity of daily life evaluations were conducted before and after the intervention. The results revealed improvements in the performance of all participants following the intensive rehabilitation training. This case study demonstrates that high-intensity rehabilitation exercise training improves the physical fitness and activity of daily life in frail elderly.