The invention relates to the field of medicine, and specifically to medicinal agents for treating arthrological diseases. The agent comprises a Na-salt of chondroitin sulfate with an intrinsic viscosity (η) of 0.01-0.04 m/kg in the amount of 4-12 wt.%, benzyl alcohol in the amount of 0.8-1.2 wt.% as a preservative agent an water as the balance. The agent may further comprise sodium bisulfite in the amount of 0.09-0.11 wt.% as a stabilizer. An injectable dosage form of chondroitin sulfate provides a desirable therapeutic effect with no side-effects such as a pain syndrome in the moment of injecting and occurrence of indurations in injection sites.