<p>Aim: To investigate the proportion of participants with levator avulsion injury among women at one month postpartum and clarify the relationship between avulsion and the area of levator hiatus. Method: This research was conducted as a secondary analysis of existing data. Avulsion injury and the area of levator hiatus were evaluated by ultrasonography in 89 women at one month after delivery. After delineating the midsagittal image transperineally, the reference axial slice at the plane of minimal distance between symphysis pubis and anorectal angle was created, and the area of levator hiatus was measured. The presence of avulsion injury was evaluated based on the three slices which were one reference axial slice of levator hiatus and two slices placed at 2.5mm slice intervals to 5.0mm cephalad from the reference slice. Result: Twelve participants (13.5%) had avulsion. Out of twelve, four had complete avulsion, defined as detachment is shown in all three slices, and remaining eight had partial avulsion, defined as detachment is shown in one or two slices. The area of levator hiatus during Valsalva maneuver was significantly larger in women with avulsion compared to those without it (median 21.36cm ² vs17.87cm ² ; p=0.037). Twelve women (13.5%) had ballooning, which is abnormal enlargement of levator hiatus (defined as the area of 25cm ² or more), and the proportion of it was significantly higher in women with avulsion injury (41.7%vs9.1%; p=0.009). Conclusion: Among women at one month postpartum, 13.5% were confirmed to have avulsion, which was relatively less than the proportion reported in previous research. In women with avulsion injury, levator hiatus was enlarged, and ballooning was detected more compared to in women without avulsion.</p>