Objective The ability of oral bacteria to adhere to tooth surface is associated with their pathogenicity. The objective of this study was to compare the ability of 4 strains of periodontal pathogens attaching to collagentreated hydroxyapatite（C- HA） beads in order to evaluate the ability of the main periodontal pathogens to form the biofilm on root surface. Methods The binding amount and binding percentage of 4 strains to C- HA were measured and compared by 3H- labeled binding assay. 4 strains of periodontal pathogens were Fusobacterium nucleatum（F. nucleatum）ATCC 10953, Porphyrin gingivalis（P.gingivalis） ATCC 33277, Prevotella intermedia（P.intermedia） ATCC 25611 and Hemophilic.actinomycetemcomitans（H.actinomycetemcomitans） ATCC 29523. Results The differences of the percentage of relative adherence between F.nucleatum ATCC 10953 and P.gingivalis ATCC 33277, as well as between H.actinomycetemcomitans ATCC 29523 and P.intermedia ATCC 25611 could not be observed. However, the percentage of relative adherence of F.nucleatum ATCC 10953 and P.gingivalis ATCC 33277 was higher than that of P.intermedia ATCC 25611 and H.actinomycetemcomitans ATCC 29523（P
