The isolated idiopathic finger flexor tenosynovitis is a rare condition, related to diversed etiologies. The traditional treatment of flexor tenosynovitis includes medications and injection of steroids. If the conservative treatment is not effective, surgical management is usually recommended. And alcohol installations have been rarely performed. We are reporting an extremely rare case of a 56-year-old man who had chronic idiopathic isolated finger flexor tenosynovitis which was treated through alcohol injections. The patient had not yet been treated despite of medication and serial injections of steroid. We performed 1 mL of 50% ethanol injection for the initial treatment and the second injection was done in the same way 10 months later due to the improvements of the patient's clinical symptoms and images of the follow-up ultrasonography. As a result, the authors suggest alcohol installation as an alternative non-surgical treatment for flexor tenosynovitis when other conservative managements are not effective enough.