Although oral health care has a preventive effect against ventilator-associated pneumonia (VAP), the most effective method of oral health care in this respect remains to be established. The objective of this single-center, randomized, controlled trial was to investigate the relationship between VAP and various methods of oral health care. All patients included in the study (n=142) were on mechanical ventilation with oral intubation at the intensive care unit of the Tokyo Dental College Ichikawa General Hospital. They were divided into two groups, one receiving standard oral health care (Standard group), and the other receiving oral health care using an oral moisture gel instead of water (Gel group). After removal of the intubation tube, biofilm on cuff of the tube was stained with a disclosing agent to determine the contamination level. Factors investigated included sex, age, number of remaining teeth, intubation time, fever ≥38.5°C, VAP, cuff contamination level, and time required for one oral health care session. No VAP occurred in either group during the study period. The level of cuff contamination was significantly lower in the Gel group than the Standard group, and the time required for one session of oral health care was shorter (p<0.001). Multivariate analysis revealed use of the oral moisture gel as a factor affecting cuff contamination level. Use of an oral moisture gel decreased invasion of the pharynx by bacteria andcontaminants together with biofilm formation on the intubation tube cuff. These results suggest that oral health care using an oral moisture gel is effective in preventing cuff contamination.