BACKGROUND Disk herniation (DH) is one of the most common disk lesions, inducing low back pain (LBP). Various therapeutic options have been proposed for treatment of disk herniation (DH). Intradiscal injection of ozone has been suggested for treatment of DH. OBJECTIVES To determine the effect of intradiscal ozone injection on pain score and disability in patients with LBP from disk prolapsed. PATIENTS AND METHODS Patients with LBP diagnosed with DH were enrolled in this clinical trial study. After prep and drape the area and under the fluoroscopy guide (c-arm), intradiscal injection of ozone/oxygen mixture (4 mL, 40 µg/mL) was performed. Pain score and functional ability of the patients according to Oswestry Disability Index (ODI) were measured prior to the injection (baseline) and then at 2 and 4 weeks and then at 3 and 6 months after the injection. RESULTS Thirty patients (17 females, 13 males) with the mean age of 58.6 y (range, 42-73 y) enrolled in the study. The mean ± standard deviation (SD) of pain score before intervention was 8.1 ± 0.8. After two weeks, it was reduced to 3.2 ± 0.6 (P < 0.001) and finally dropped to 2.0 ± 0.6 sixth months after intervention (P = 0.0001). Functional status of ODI was 28.5 ± 2.1 before intervention and showed significant reduction after two weeks (with the mean of 12.3), and it was almost sustained till sixth months after intervention, with the mean of 11.4 (P = 0.001). CONCLUSIONS Altogether, ozone had significant positive effects on patients with disk herniation unresponsive to other conservative and minimally invasive treatments.