Schwannomas are benign tumors arising from the peripheral nerves with a Schwann cell sheath. Schwannomas can be found in almost every region, but are usually associated with cranial, spinal, sympathetic and peripheral nerves. Schwannoma in lower extremity is relatively common and most are associated with sciatic nerve, peroneal nerve and tibial nerve. However, schwannoma arising in the tendon or paratenon is extremely rare. We report a rare case of a 25-year-old male patient with a schwannoma originating from the paratenon of semitendinosus muscle without evidences of any neurologic symptoms. The clinical history, plain radiographs, magnetic resonance imaging, and pathologic findings of the reported patient have been reviewed. The tumor was fully excised by dissecting a tendon sheath of semitendinosus muscle.