NOVELTY - Antibacterial hydrogel comprises water, hyaluronic acid derivative and antibacterial agent. The hyaluronic acid derivative comprises hyaluronic acid or its salt, having molecular weight of 50000-3500000 Da grafted with chains of biodegradable and biocompatible polyester having molecular weight of 3000-900000 Da. The concentration of the hyaluronic acid derivative or its salt is 1-30 weight/volume%. The antibacterial agent is chosen from antibiotics and/or metal ions. The concentration of the antibacterial agent is 0.001-80 weight/volume%.    USE - The antibacterial hydrogel is useful for region of bone fracture or cavity, producing antibacterial coating on prosthesis useful for implantation into human or animal (all claimed) and in orthopedic surgery.    ADVANTAGE - The hydrogel has excellent chemical and mechanical stability, and can be stored for at least six months even at ambient temperature. The release of the antibacterial agent is improved.    DETAILED DESCRIPTION - Antibacterial hydrogel comprises water, hyaluronic acid derivative and antibacterial agent. The hyaluronic acid derivative comprises hyaluronic acid or its salt, having molecular weight of 50000-3500000 Da grafted with chains of biodegradable and biocompatible polyester having molecular weight of 3000-900000 Da, such that the derivative comprises 1-15 polyester chain/100 D-glucuronic acid/N-acetyl-D-glucosamine repeating units of hyaluronic acid. The concentration of the hyaluronic acid derivative or its salt is 1-30 weight/volume%. The antibacterial agent is chosen from antibiotics and/or metal ions. The concentration of the antibacterial agent is 0.001-80 weight/volume%. INDEPENDENT CLAIMS are included for the following:    (1) method for using the antibacterial hydrogel, involves producing the antibacterial hydrogel just before use by mixing hydrogel comprising hyaluronic acid derivative and water with the chosen antibacterial agent (antibiotic), in desired ratio;    (2) kit for producing the antibacterial hydrogel, comprising composition comprising hydrogel formed using hyaluronic acid derivative (1-35 weight/volume%) and water, and composition being or comprising antibacterial agent; and    (3) prosthesis for implantation into human or animal, coated with the antibacterial hydrogel.