The present invention addresses the problem of providing a disinfectant solution that is prepared by coloring an aqueous olanexidine gluconate solution, said solution being a colorless and transparent liquid, and, therefore, can facilitate the confirmation of an area to which the disinfectant solution is applied for preoperative disinfection etc.A disinfectant solution capable of facilitating the confirmation of an area to which the disinfectant solution is applied for preoperative disinfection etc., can be prepared by using olanexidine gluconate, a coloring agent such as Sunset Yellow FCF and an alkyldimethylamine oxide such as lauryldimethylamine oxide, optionally together with one or more kinds of surfactants other than alkyldimethylamine oxides, for example, a polyoxyethylene alkyl ether such as lauromacrogol and a polyoxyethylene polyoxypropylene alkyl ether such as polyoxyethylene(20) polyoxypropylene(4) cetyl ether.
