FIELD : medicine; pharmaceuticals.SUBSTANCE : present invention refers to pharmaceutical industry, namely to a composition for treating osteoarthritis. Composition for treating osteoarthritis for intraarticular administration containing hydrophilised sulphasalazine as an active ingredient in a certain amount. Method for preparing a composition for treating osteoarthritis for intraarticular administration, comprising a step for preparing an aqueous solution of polyethylene glycol (PEG), having pH from 11 to 14, by dissolving the basic additive and PEG in water and dissolving sulfasalazine in said aqueous solution; stage of hyaluronic acid dissolution, its salt or cross-linked hyaluronic acid in the product and a step for neutralizing the product with the help of an acid additive, where the main additive is one or more selected from a group consisting of sodium hydroxide, potassium hydroxide and ammonia from 0.01 to 1 wt.?%/vol. Composition for treating osteoarthritis suitable for intra-articular injection, prepared by the disclosed method. Method for reducing the development or treatment of osteoarthritis, comprising a stage of intraarticular administration of a composition containing hydrophilised sulphasalazine as an active ingredient taken in a certain amount.EFFECT : disclosed composition prepared by the disclosed method is effective for treating osteoarthritis in intra-articular administration.9 cl, 5 dwg, 5 ex