Abstract: The present invention provides a medical composition which, in autotransplantation which is the only method that can induce the epithelialization even in a widespread full-thickness skin defect, enables the fixation of an autotransplantation skin graft in a simple manner and can increase the efficiency of epithelialization to promote the regeneration of the skin. The present invention elates to a medical composition comprising a photo-crosslinkable chitosan derivative and an amino acid and/or a saccharide. The amino acid is preferably an essential amino acid, and the saccharide is preferably a neutral saccharide selected from glucose, galactose, mannose and fucose.