Purpose The purpose of this study is to confirm the change in the thickness of transverse abdominal muscles during bridge exercise on the unstable support surface BOSU ball and sling, and to suggest a new method for core stabilization exercise. Method Twentyfour people participated in this study, divided into a BOSU ball group (n=12) and a sling group (n=12). A bridge exercise was performed both group respectively. Each exercise was repeated five times for 40 seconds, and a 20second rest period was given between experiments. The knee joint angle was set to 90 degrees. Results Both groups showed a statistically significant increase after exercise. However, there was no statistically significant difference in the average increase in the thickness of transverse abdominal muscles between the BOSU ball group and the sling group. Conclusion The bridge exercises on an unstable support surface using a BOSU ball or using a sling help improve the thickness of transverse abdominal muscles in healthy adults. Therefore, we would recommend using BOSU balls and slings appropriately according to the situation.