This study was designed to determine the efficacy of ultrasound and laser therapy for sub-acute lower back pain. Twenty-seven patients with sub-acute low back pain were recruited, who were randomly assigned to three groups: Ultrasound group (actual ultrasound, 1.1 MHz, $1.0W/cm^2$, duty cycle 100%, 10 min/session, n=9), laser group (actual laser, 904 nm, 155 ns, 13.5 W, 12 mW, 90 sec/point, n=9), and control group (placebo ultrasound or placebo laser, n=9). All of treatments including placebo procedures were applied to patients over a period of 2 weeks, five times a week. Visual Analogue Scale (VAS), Modified Schober's Test (MST), and Modified Oswestry Disability Questionnaire (MODQ) were used by the clinical and functional evaluations before and after intervention. At post-hoc, significant differences were observed in all groups with respect to VAS, MST (p<.05), except MODQ. VAS and MST score were more significantly improved in the ultrasound group than the laser and control group (p<.0167). However, no significant difference was present between the laser group and the control group. Therefore, this study revealed that ultrasound therapy was effective in pain relief and improvement of lumbar mobility in patients with sub-acute lower back pain. However, laser therapy did not show the effects for sub-acute lower back pain.