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.
