A 34-year-old female was suffered from pain and numbness of right arm for 2 months after undergoing a thoracoscopic procedure for a posterior mediastinal mass that was diagnosed as neurilemmoma. The patient was diagnosed as a complex regional pain syndrome type 2 with brachial plexopathy developed during thoracoscopic excision of posterior mediastinal mass, and stellate ganglion block (SGB) with 0.2% ropivacaine 10 mL was performed every 3-4 days. The patient revealed slightly prolonged blepharoptosis as Horner syndrome accompanied after every SGB and recovered. However, following the 23rd SGB, the blepharoptosis persisted and patient was recovered spontaneously from blepharoptosis after about 12 months. The possibility that the persistent blepharoptosis might be caused by brachial plexopathy related to patient's pathology or surgical manipulation and/or repeated SGB. If Horner syndrome occurs, its etiology should be assessed, and it would be necessary to explain and to assure the patient the possibility of recovery spontaneously from the complication within a year, without any sequelae.