This study was conducted to assess the potential of chlorhexidine for use in the prevention and treatment of dental caries, and to investigate its effect on the development of dental caries. The study enrolled patients without systemic disease or drawbacks with data collection. They visited the M Dentist Office located in Busan from September 2014 to January 2015. They were equally divided into three groups. The subjects in group X1 gargled with 15 ml of 0.9% saline solution (JW Pharmaceutical Corporation) for about one minute while the subjects in group X2 gargled with 15 ml of 0.005% chlorhexidine (Bukwang Pharmaceutical Co., Ltd.) for about one minute. After the subjects spit out saliva for one minute to remove the remaining gargling solution, the simplified oral hygiene index (S-OHI) was measured again, along with the amounts of coccus and inactive bacteria, again through the Alban test and the phase-contrast microscope. For a comparison of the amounts of coccus and inactive bacteria that were quantitatively analyzed with a program that analyzes the microorganisms observed under a phase-contrast microscope, the S-OHI, and the Alban test result between the saline solution and chlorhexidine groups, student t-tests were conducted at p=0.05. As a result, there was no significant difference between two groups but a significant difference between two groups found after gargling. To prevent dental caries, oral management controlling the biofilm on the tooth surface, reducing activity of coccus, and decreasing the acid production ability of bacteria is necessary. Therefore, this study implies that use of chlorhexidine gargling alone greatly contributes to prevention of dental caries as well as inhibition of attachment of the biofilm on the tooth surface.