Background: Diastasis rectus abdominis (DRA) involves the separation of the midline abdominal muscles and linea alba and affects more than half of postpartum women. This study aimed to assess the effect of a split tummy exercise program (STEP) on DRA closure in postpartum mothers. Methods: A randomized controlled trial was conducted from 2008 to 2020 at the Obstetrics and Gynaecology Clinic of the Universiti Kebangsaan Malaysia Medical Centre. Primigravida mothers diagnosed with DRA were selected and randomly assigned to the intervention (n=21) or control (n=20) group. The intervention group underwent a home-based STEP consisting of three phases of nine abdominal exercises. DRA size was assessed at baseline and at 8 weeks postpartum using two-dimensional ultrasound. Results: The mean age of the participants was 28 years (standard deviation, 3.6), with the majority of Malay ethnicity (87.8%) and working mothers (78%). After 8 weeks, the intervention group showed a significant reduction in DRA size of up to 27% (mean difference, 6.17 mm; 95% confidence interval, 3.7–8.7; P<0.001). No significant intergroup DRA changes were observed after 8 weeks of follow-up. Conclusion Early postpartum screening for DRA should be advocated to allow early STEP intervention to ensure favorable outcomes. STEP intervention is an effective postnatal training program for managing DRA.