Serotonin syndrome (SS) is an adverse drug reaction characterized by neuromuscular hyperexcitability that is mild in most cases but can be life-threatening in some cases. This paper reports a case of a 87-year-old man with Parkinson’s disease who was hospitalized due to pulmonary infection and fever. The clinical symptoms were improved after treatment. Subsequently, his condition fluctuated, including high fever, sweating, disturbance of consciousness, high muscle tone and elevated creatine kinase. After combining his clinical manifestations with his history of concomitant medication, the doctors found that the patient had overdosed on selegiline and had an adverse reaction with anti-infective drug linezolid. The patients was diagnosed having SS promptly and was treated actively and properly, including discontinuation of related medications, and physical cooling, extensive fluid rehydration, and symptomatic supportive treatment. Thus the patient’s condition was effectively controlled within 24 hours. The symptoms were basically improved 3 days after onset and completely relieved 5 days after onset. Prevention is the key point to SS, and clinicians should strengthen their awareness.