We report a rare complication of cervical laminoplasty in cervical ossification of the posterior longitudinal ligament (OPLL). A 69-year-old man suffered from gait disturbance and numbness of the bilateral hand for 6 months. He underwent C3-7 partial laminoplasty at the department of orthopedic surgery. After the operation, his symptoms immeadiately disappeared. However 1 month later, he presented with memory disturbance and gait disturbance. A computed tomography (CT) scan of head showed hydrocephalus, and cervical magnetic resonance imaging (MRI) showed fluid collection in the epidural and subcutaneous spaces. A ventriculoperitoneal shunt was performed, and it resolved the memory and gait disturbance. This is the second case report of hydrocephalus after laminoplasty for cervical OPLL.