Abstract.[Purpose] The purpose of this study was to identify the changes in abdominal muscle thickness during the abdominal drawing-in maneuver (ADIM) in patients with low back pain (LBP) and healthy subjects.[Subjects] The subjects were 40 volunteers: 20 healthy subjects and 20 patients with LBP. [Methods] In sitting, the subjects performed rest for 10 seconds and ADIM for 10 seconds as a set with 3 repetitions. Thickness measurements of the abdominal muscles were performed in triplicate while subjects were at rest and performing ADIM using B-mode ultrasound imaging.[Results] In patients with LBP there was no significant change in the thickness of the external oblique (EO), whereas the EO of healthy subjects significantly decreased during ADIM. The thickness of the internal oblique (IO) and transversus abdominis (TrA) significantly increased during ADIM as compared to at rest in both groups.[Conclusion] These findings suggest that ADIM increase the thickness of the deep abdominal muscles and that the change in the thickness of the deep abdominal muscles of patients with LBP increase less than that of healthy subjects. Therefore, ADIM should be used to train the deep abdominal muscles of patients with LBP.