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.
