Objective To analyze pathologic features and surgical procedures for patients with unroofed coronary sinus syndrome (UCSS) associated with endocardial cushion defect (ECD). Methods The clinical data of 44 patients with UCSS and ECD from May 1998 to July 2016 were retrospectively reviewed. There were 18 males and 26 females with a mean age of 10.4±12.1 years (range: 5.0 months to 44.0 years) and mean weight of 25.2±20.9 kg (range 5.2-80.0 kg). According to the Kirklin and Barratt-Boyes classification, 28 patients were categorized into type Ⅰ, 5 typeⅡ , 4 type Ⅲ and 7 type Ⅳ. Among them 25 patients suffered partial ECD, 10 complete ECD, 9 transitional ECD, and 27 were associated with single atrium, 34 involved persistent left superior vena cava (PLSVC), and in 27 of the 34 patients PLSVC directly drained into the left atrium (LA). Among the 44 patients, 1 patient associated with complex anomalies underwent palliative operation, and other cardiac malformations were corrected simultaneously by surgical correction. PLSVC was ligated in 2 patients, and the intracardiac tunnels or baffles to drain PLSVC to right atrium (RA) were reconstructed in 25 patients. The associated cardiac lesions were corrected concomitantly. Results In-hospital death occurred in 2 patients, among whom 1 died of low cardiac output syndrome on postoperative day 8 and the other pulmonary infection on postoperative day 21. Thirty-one were followed up from 1 month to 10 years, and there was no death or severe complications. Conclusion When ECD is associated with PLSVC and a single atrium, UCSS may develop. Repair according to the type of UCSS is effective.