The purpose of this study was to investigate the effect of wearing the removable partial denture on plaque accumulation. Twelve removable partial denture cases were examined. Patients were recalled three consecutive 3 day periods. Plaque index was measured after each 3 day period. (1) not wearing the denture, (2) wearing the denture, (3) wearing the denture after intensive tooth brushing instruction. The results were as follows: 1. Plaque indices of all the remaining teeth were higher following the wearing of removable partial denture than those of teeth not wearing the denture and those of teeth after intensive tooth brushing instruction. 2. Plaque indices showed statistical difference between all the tooth surfaces which were in contact with the denture and those which were not. 3. Plaque indices showed no statistical difference between buccal and lingual surfaces which were in contact with the denture and those which were not. 4. Plaque indices showed statistical difference between proximal surfaces which were in contact with the denture and those which were not.