Purpose: Carpal tunnel syndrome (CTS) is the most common entrapment neuropathy in the upper limb. Local injection of different substances has been increasingly used as an acceptable conservative treatment in non-severe cases. This study aimed to evaluate the efficacy and safety of local ozone injection in the management of non-severe CTS. Methods: In the current randomized controlled trial (RCT), 40 patients with mild or moderate CTS were included in two parallel groups. Both of them used the resting volar wrist splint for 8 weeks; while the intervention group received a single dose of local ozone injection, except for the same splinting protocol. The main outcome measures including visual analog scale (VAS) for pain; symptom severity or functional status, based on Boston questionnaire (BQ); and median nerve conduction study, were reassessed 10 weeks after the treatment. Results: All of the measures including VAS, symptom severity, functional status and EDX improved significantly in both groups with the maximal changes in VAS. The VAS reduction was more remarkable in the ozone group than the control group [64% versus 45.3%, respectively]. Moreover, both of the BQ subscales showed significantly higher improvement in the ozone group compared to the control group ( P =0.01 and 0.02, respectively). Although the improvement of EDX parameters was slightly better in the ozone group, the difference was not significant. Neither minor nor major side effects were reported. Conclusion: Ozone therapy as a safe and low-cost method, could provide promising results among women with mild to moderate CTS, at least for short-term treatment. Clinical trial registration: IRCT2016040913442N9.