Horner syndrome is caused by damage of the oculosympathetic pathway. It is a common disorder characterized by ocular signs such as ptosis and miosis, and these signs usually indicate the occurrence of severe head, neck and chest diseases or surgical complications. We report a case of 49-year-old male patient who underwent parapharyngeal space tumor resection in the Department of otolaryngology. On postoperative day one, the patient presented right eyelid drooping, the right pupil constricted, and the absence of sweating on the right side of the face. After six months of follow-up, the above signs still presented and showed no significant change. T??he pathological assessment of the resected parapharyngeal space tumor demonstrated that it is the sympathetic trunk schwannoma, which is relatively rare in clinical practice.