To assess the efficacy and safety of naproxen in patients with nonspecific low back pain.Ninety patients with nonspecific low back pain were enrolled in the study. Patients took 550 mg of naproxen twice a day. All patients were assessed with VAS, the Oswestry questionnaire, Schober's test and clinical global impression scale. The treatment lasted from 7 to 14 days depending on the pain relief (VAS ≤10 mm).The pain syndrome relief was observed in 77 patients (88.5%) during the first week of the treatment and in 81 (93.1%) by the end of the study. The average value of VAS was reduced by 6.2 times (by 52.9 mm) in comparison to the baseline. According to the Oswestry questionnaire the influence of pain syndrome on the life quality was reduced by 4,78 times in comparison to the baseline. Schober's test revealed an increase in the amplitude of movements during therapy by 27% in comparison to the baseline. Only 5 (5.7%) drug-related adverse reactions were observed during the whole study, 80% of those were mild.Naproxen in the dose of 550 mg twice a day demonstrates the high efficacy and safety in patients with non-specific pain in lumbosacral spine.