The lumbar multifidus muscle, which can be separated into deep fascicles (DM) and superficial fascicles (SM), is important for lumbar segmental stability. However, no previous studies have investigated the effect of lumbar stabilization exercises on the thickness of DM and SM. Thus, the purpose of this study was to assess DM thickness after three different lumbar segmental stabilization exercises. In total, 30 healthy male participants were recruited and randomly assigned to one of three exercise groups: hollowing in the quadruped position (H-Quad), contralateral arm and leg lift (CALL), and bilateral arm and leg lift (BALL). Each lumbar segmental stabilization exercise was conducted over 4 weeks. Ultrasonography was used to compare the DM and SM thickness before and after the 4 weeks of exercise. A mixed-model analysis of variance using Scheffe's post-hoc test was used for statistical analysis. The results showed a significant effect for the measurement time (before vs. after 4 weeks of exercise) in the DM (F=31.26, p