Background: Previous researchers have investigated the mechanical and neurophysiological effects of manual mobilization, however little research has been done on muscle tone and muscle stiffness. Objective: To compare the effects of posterior-anterior (PA) mobilization with weight bearing on sling and conventional PA mobilization on the bed. Design: Randomized controlled trial (single blind) Methods: The subjects were 16 male university students and randomized to sling mobilization group (SMG, n=8) or conventional mobilization group (CMG, n=8). SMG received PA mobilization using a sling and CMG received traditional mobilization on the bed during lumbar mobilization. Results: Both left and right muscle tones of SMG increased, but left muscle tone of SMG were increased and right muscle tone was decreased after intervention. In addition, both left and right muscle stiffness of SMG were also increased, however left muscle stiffness of SMG was increased and right muscle stiffness was decreased. The muscle tone and muscle stiffness of SMG were higher than those of DMG, especially the right side was statistically significantly higher. Extension of SMG, extension and flexion of CMG were increased statistically significantly except for Flexion of SMG (p<.05). There were no significant differences between the groups in Extension and Flexion. Conclusions: This study suggests that lumbar spine PA mobilization using sling is beneficial in improving muscle tone, muscle stiffness, and trunk movement.