We investigated the long-term effects of comprehensive hand repetitive intensive strengthening training (CHRIST) on strength, morphological muscle size, kinematics, and associated motor functional changes in children with cerebral palsy (CP). Ten children (5 boys, 5 girls; age range, 6-11 years, mean age, 8.6 years) participated in the study. The children were classified according to the Manual Ability Classification System: 5 were Level II, 2 were Level III, and 3 were Level IV. Quantitative biomechanical measurements were performed to determine muscle strength, muscle size, kinematics (normalized jerk score), and motor function using a dynamometer, ultrasound, Vicon motion analysis, and standardized clinical tests (Quality of Upper Extremity Skills Test, Jebsen-Taylor Hand Function Test, Functional Independence Measure, and Pediatric Motor Activity Log), respectively. Muscle strength, muscle size, kinematics, and motor function significantly improved after a 10-week intervention (3 times a week), and the long-term effects remained even at the 3-month follow-up. In conclusion, this is the first study highlighting the long-term efficacy of upper extremity strength training using the novel CHRIST system in children with CP, which will potentially open up new horizons for effective management in pediatric neurorehabilitation.