OBJECTIVE The aim of this study was to report our clinical experience of applying a uterine flexion suture, which was modified from the B-Lynch uterine compression suture, for treating uterine atony during cesarean section. METHODS This is a retrospective descriptive study describing the use of a new technique, uterine flexion suture, for treating uterine atony during cesarean section. The study period was from January 2009 to December 2017 at Udonthani Hospital, Udonthani, Thailand. Uterine atony during cesarean section was treated by manual compression, intravenous oxytocin, methylergonovine maleate, and prostaglandins and then was observed for 10-15 minutes before applying a uterine flexion suture in the failed medical treatment cases. The patients were observed for vaginal bleeding, hematometra, and infection after operation. Uterine ultrasound scan results on days 1, 7, and 30 postoperation were also reviewed. RESULTS Fifty-seven patients with uterine atony during cesarean delivery received the uterine flexion suture. The mean age of patients was 27.0 (15-44 years). Thirty-four patients were primipara. The indications for cesarean section were cephalopelvic disproportion in 27 (47.4%) cases, and previous cesarean section in 11 (19.3%) cases. Neither postoperative excessive bleeding nor hysterectomy was observed. There was no hematometra or serious postoperative complication after surgery. The estimated time for uterine flexion suture is only 2-3 minutes and was very easy to perform. CONCLUSIONS Uterine flexion suture technique, which was modified from the B-Lynch suture, was inexpensive, quick, and effective in the treatment of atonic postpartum uterus in women undergoing cesarean section.