Purpose: The purpose of this study was to compare the effects of oral hygiene with 0.1% chlorhexidine or with normal saline on the incidence of pathogens in the oral cavity of patients in Intensive Care Units (ICU). Method: A quasi experimental design with non-equivalent control group and non-synchronized design was used. For the study 46 patients were recruited from a university hospital (24 for the experimental group, 22 for the control group). patients in the experimental group received mouth care with 0.1% chlorhexidine gluconate and those in the control group received mouth care with normal saline twice a day for 7 days in a row. Oral samples were taken for bacterial cultures on admission day, the 4th day and the 7th day for both groups. Results: The incidence of oral pathogens decreased in the experimental group, and increased in the control group. There was no significant difference in the incidence of oral pathogens between the two groups. However oral hygiene using 0.1% chlorhexidine gluconate decreased the incidence of oral pathogens significantly for patients who already had pathogenic bacteria in their mouths on the admission day. Conclusion: The results suggest that mouth care with 0.1% chlorhexidine is effective for decreasing the incidence of oral infection for ICU patients who have oral infections.