Objective To investigate the effectiveness of transurethral resection of ureterocele in the treatment of hydronephrosis or hydroureter caused by duplex kidney and deformity of ureter combined with ectopic ureterocele. Methods Nine patients with duplex kidney and deformity of ureter combined with ectopic ureterocele, who were admitted to The First Affiliated Hospital of the Naval Medical University (Second Military Medical University) from Jan. 2013 to Jun. 2021, were enrolled, including 3 patients suffered from lumbago, 2 patients suffered from dysuria, and 2 patients suffered from recurrent urinary tract infection. All patients were diagnosed by urinary ultrasound, intravenous urography, enhanced computed tomography urography, and cystoscopy before operation. All patients underwent transurethral resection of ureterocele. Results The operation was performed successfully on all patients. The operation time was 20-40 min, with an average of (28.3±7.5) min, and the average intraoperative bleeding was less than 20 mL. Double-J stent insertion was used in 3 patients during the operation. The drainage fluid in bladder irrigation was limpid, and bladder irrigation was stopped within 24 h after surgery. The catheters were removed and patients were discharged 2-3 d after surgery. The average postoperative hospital stay was (2.4±1.6) d. The double-J stent was removed 6-8 weeks after the operation. The patients were followed-up after postoperative 1-24 months with ultrasound examination, and all hydronephrosis was relieved, except 3 patients who still had mild hydronephrosis. The symptoms such as soreness of loins, lumbago and dysuria disappeared, and there was no recurrence of urinary tract infection. Conclusion Transurethral resection of ureterocele has advantages of minimal invasion, quick recovery, few complications and high acceptance of patients. It can be the first choice for patients with duplex kidney and deformity of ureter combined with ureterocele with surgical indications.