Objective. To assess analgesic properties of melatonin in the treatment of chronic non-specific low back pain and to study predictors of its efficacy. Material and methods. A study included 178 patients, aged from 40 to 65 years, with chronic non-specific low back pain during >3 month and the VAS score >3. Patients were stratified into 6 groups (3 pairs of comparison). In the first pair, patients of both groups received a combination of 500 mg of glucosamine hydrochloride and 500 mg of chondroitin sulfate; in the second pair — a combination of 500 mg of glucosamine hydrochloride and 500 mg of chondroitin sulfate and diclofenac, in the third pair — diclofenac. All patients received additionally melaxen. The duration of the study was 3 month in the first pair and one month in the second and third pairs. With regard to response to melatonin, patients of the main groups were divided into responders and non-responders. Baseline factors determining the efficacy of treatment with melatonin were studied. Results and conclusion. A significant reduction in pain intensity at movement and resting state was noted in all main groups compared to comparison groups. This result indicates possible analgesic properties of melatonin. Moreover, factors predicting the efficacy of such therapy were determined. Addition of melatonin to the standard scheme of low back pain treatment increases its efficacy, in particular in case of comorbidity of pain and sleep disorders and depressive symptoms.