BACKGROUND: Manual therapy has been recommended to reduce and prevent musculoskeletal problems related to thoracic hyperkyphosis. With recent rapid technological developments, manual techniques can now be implemented by mechanical devices; hence, mechanical massage can manipulate the back muscles and mobilize the spine. PURPOSE: Here, we aimed to 1) determine the effects of mechanical massage and manual therapy and 2) compare their effects on spinal posture, extension range of motion, trunk extensor electromyographic activity, and thoracic extension strength in individuals with thoracic hyperkyphosis. METHODS: Participants with thoracic hyperkyphosis were randomly assigned to the manual therapy ( = 16) or mechanical massage ( = 19) group. Each intervention was applied for 8 weeks. The participants' spinal posture, extension range of motion, trunk extensor electromyographic activity, and thoracic extension strength were measured before and after intervention. RESULTS: Intergroup analyses revealed no significant differences in any variables. However, thoracic kyphosis angle, thoracic extension range of motion, longissimus thoracis electromyographic activity, iliocostalis lumborum pars lumborum activity, and thoracic extension strength differed significantly in intertime analyses. The results of paired -test analysis showed that thoracic kyphosis angle, thoracic extension range of motion, longissimus thoracis electromyographic activity, and thoracic extension strength were significantly different after intervention in both groups ( < 0.05). CONCLUSIONS: Mechanical massage and manual therapy effectively improve thoracic kyphosis angle, thoracic extension range of motion, and thoracic extension strength. Therefore, mechanical massage is an alternative intervention to manual therapy for improving thoracic kyphosis angle, thoracic extension range of motion, and thoracic extension strength in participants with hyperkyphosis. This trail is registered with KCT0004527.