Red complex bacteria (, , and ) have high virulence in periodontal disease. In the present study, we aimed to elucidate the detailed symbiotic relationships between the red complex and other oral bacteria in older Japanese individuals. Polymerase chain reaction was performed using dental plaque from 116 subjects and specific primers for ten periodontal pathogens. The detection rate of and was significantly higher in -positive subjects than in -negative subjects ( < 0.05). The detection rate of , , , and was significantly higher in -positive subjects than in -negative subjects ( < 0.01). In a comprehensive analysis of oral microbiomes, three red complex species-positive subjects had significantly higher α-diversity than only -positive subjects ( < 0.05) and had significantly lower β-diversity than only -positive subjects ( < 0.01). In the taxonomy analysis, was significantly higher in three red complex species-positive subjects than in only -positive and only -positive subjects ( < 0.01). These results suggest that each red complex species forms a unique oral microbiome and individuals positive for all red complex bacteria may harbor oral bacteria that confer a significant advantage in developing periodontal disease.