Objective: To evaluate the utility of transurethral seminal vesiculoscopy with a slender ureteroscope in the treatment of severe oligoasthenozoospermia secondary incomplete ejaculatory duct obstruction (EDO). Methods: From March 2018 to September 2018, the clinical data of 8 patients with severe oligoasthenozoospermia secondary incomplete EDO treated by the technique of transurethral seminal vesiculoscopy in the Peking University Third Hospital Reproductive Center were analyzed. Preoperative routine included semen analysis, hormone determination, transrectal ultrasonography, pelvic magne-tic resonance examination and other examinations. All the patients were diagnosed with severe oligoasthenozoospermia secondary to incomplete EDO. All the patients were operated by the same surgeon with multiple cases of experience in transurethral surgery, and 1 year follow-up was conducted to evaluate the surgical effect. Results: The average age of the 8 patients was 29 years, and the average operation time was 32 min. Preoperative transrectal ultrasound indicated 6 cases of ejaculatory duct cyst or Mullerian cyst, 1 case of prostate calcification and bilateral seminal vesicle dilatation. The average maximum transverse diameter of the right seminal vesicle in pelvic MRI was 33.60 mm (24.63-42.28 mm), the average maximum transverse diameter of the left seminal vesicle was 32.85 mm (25.91-44.89 mm), the ave-rage maximum antero-posterior diameter was 27.99 mm (21.36-33.12 mm), the average maximum width of the seminal vesicle duct was 10.53 mm (5.93-19.39 mm). There were 5 cases of ejaculatory duct cyst, 2 cases of seminal vesicle hemorrhage, and 1 case of Mullerian cyst. The semen volume [(2.64±0.80) mL], the sperm concentration [(49.76±8.50)×10⁶/mL], and the motility (grade a+b) [(25.76±6.48)%] in postoperation were significantly higher than those in preoperation [(1.46±0.50) mL, (28.78±5.17)×10⁶/mL, and (2.88±0.93)%, P<0.05]. Two patients conceived naturally during the follow-up of 6 months after surgery. There were no severe complications, such as retrograde ejaculation, urinary incontinence or rectal injury. Conclusion: The technique of transurethral seminal vesiculoscopy is safe and effective for treating severe oligoasthenozoospermia secondary to incomplete EDO. However, due to the small sample size of this study, short follow-up time, and the uncertainty in seminal vesicle surgery, it still needs to be further confirmed by long-term follow-up studies with large samples.