Objective. To study the efficacy and safety of chondroitin sulfate (mucosat) in the treatment of chronic lower back pain. Material and methods. The medical documentation of 46 outpatients with chronic lumbosacral dorsalgia, who received 25 intramuscular injections of 2 ml mucosat, was studied. The assessment of patients' condition and efficacy and safety of the treatment was conducted based on the data of four visits (1-st, 10-th and 25-th day and 3 months after the end of treatment). Results of the clinical-neurological examination, pain intensity at rest and at movement according to the Visual Analogue Scale (VAS) and the severity of Lasegue and Wasserman signs and limitation of movements in the lumbar spine were taken into account. Results. The use of mucosat at a dose of 2 ml intramuscularly 1 time in 2 days led to a significant decrease in the severity of pain syndrome and increased mobility in the lumbar spine (before treatment, the level of pain at rest according to the VAS was 4.22±1.28 scores, on the 25-th day 2.13±0.24, 3 month after treatment 2.37±0.31; the level of pain at movement: 5.78±1.15; 4.56±0.47; 4.78±0.22, respectively (p<0.01). There were a reduction of the dose of previously used non-steroidal anti-inflammatory drugs in the end of treatment and maintenance of the results of therapy for 3 months after the end of treatment. Good tolerability of the drug and the absence of significant side-effects were shown as well. Conclusion. This study showed the efficacy and safety of chondroitin sulfate (mucosat) in the treatment of outpatients with chronic lower back pain.