Various studies related to therapeutic horseback riding have been reported to be positive for the therapeutic effect of patients with cerebral palsy; however, most of the previous studies focused on to muscle development with training period related to the physical effects of therapeutic horseback riding. To identify the causes and phenomena of muscular activation of the body through actual therapeutic horseback riding exercise and to promote the excellence of physical effects of therapeutic horseback riding. This study was a nonrandomized prospective positive-controlled trial design. Twelve teenaged males with cerebral palsy were selected who had experienced riding exercise for 8-12 months. This study measured 8 muscle activities of the pectoralis major muscle (PM), biceps brachii (BB), rectus abdominis muscle (RA), latissimus dorsi muscle (LD), spinal erector muscle (SE), rectus femoris muscle (RF), anterior tibial muscle (AT), and external gastrocnemius muscle (EG) by using electromyography (EMG). Muscle activity was significantly higher in horse riding position than sitting on the common chair in all muscles (PM, BB, RA, LD, SE, RF, AT, and EG). The activity of the body muscles according to the difference of horse walking method (walk: WA; sitting trot: ST; and riding trot: RT) of therapeutic horse riding showed the highest muscle activity in the PM muscle at ST, and the highest activity at BB, RA, LD, SE, and AT muscles at ST and RT, and showed the highest muscle activity in RF and EG muscle at RT. The results of this study suggest that intervention for the treatment of cerebral palsy patients can use therapeutic riding exercise as a rehabilitation method.