The purpose of this study was to evaluate the susceptibility of anaerobic microorganisms to certain antibiotics and root canal cements. Prevotella intermedia(Bacteroides intermedius) ATCC 25611(serotype A), Fusobacterium nucleatum ATCC 25586, Actinomyces viscosus ATCC 15987 which are the predominant pathogenic anaerobes in dental root canals were cultured in BHI for 48 hours(Fig.1). After each $200{mu}l$ of those broths with microorganisms was streaked on each surface of blood agar plate, 2 to 5 antibiotic discs which are impregnated with Tetrncycline, Erythromycin, Ampicillin, Clindamycin, or Vancomycin were applied on each surface of blood agar plate and cultured for 5 days anaerobically in the anaerobic chamber<Coy anaerobic chamber MI, USA> (Fig.2). 15 antibiotic discs for each kind of antibiotics and each species of microorganisms were tested. Also each kind of root canal cement tubes which include Zinc oxide eugenol cement, Zinc phosphate cement, Calcium hydroxide powder+DD.W., Calcium hydroxide paste(Pulpdent Tempcanal), or Vitapex(Table 1) were applied on the inoculated BAPs after $200{mu}l$ of each experimental species of microorganisms was streaked on the surface of blood agar plates, and they were cultured for 5 days anaerobically in the anaerobic chamber(Fig.3). The sensitivity(antimicrobial effect) was determined by the diameter of the inhibition zone. The results are as follows: 1. The results of antibiotic susceptibility test(Table 2) 1) All of the tested antibiotics had antimicrobial activity with various degrees. 2) In Prevotella intermedia (old Bacteroides intermedius), the diameter of inhibition zone to Erythromycin($37.87mm{pm}2.20$) was largest, those to Tetracycline($26.20mm{pm}2.96$), Vancomycin($21.53mm{pm}1.96$), Clindamycin($18.73mm{pm}0.96$) was smaller than former orderly, and That to Ampicillin ($7.87mm{pm}0.83$) was smallest. 3) In Actinomyces viscosus, the diameter of inhibition zone to Erythromycin($28.73mm{pm}1.22$) was largest, those to Ampicillin($21.73mm{pm}1.03$), Clindamycin($21.33mm{pm}1.59$) was similarly next order, that to Vancomycin($19.00mm{pm}1.96$) was smaller than Clindamycin, and that to Tetracycline($11.93mm{pm}0.70$) was smallest. 4) In Fusobacterium nucleatum, the diameter of inhibition zone to Ampicillin($31.07mm{pm}1.91$) was largest, that to Erythromycin($28.87mm{pm}0.92$), Clindamycin($20.47mm{pm}1.51$), Vancomycin ($16.73mm{pm}0.96$), Tetracycline ($12.13mm{pm}1.06$) are smaller than former orderly. 2. The results of root canal cements and pastes(Table 3) 1) The external diameter of tube is 4mm, so 4mm of the inhibition zone diameter means non-susceptable. Prevotella intermedia (old Bacteroides intermedius) was non-susceptable to Calcium hydroxide powder+D.D.W., Calcium hydroxide paste(pulpdent Tempcanal), and Actinomyces viscosus was non-susceptable to Zinc phosphate cement, Calcium hydroxide powder + D.D.W., Calcium hydroxide paste(pulpdent Tempcanal). 2) In Prevotella intermedia (old Bacteroides intermedius), the diameter of inhibition zone to Zinc oxide eugenol cement($13.67mm{pm}3.30$) was largest, that to Vitapex($9.20mm{pm}2.96$), Zinc phosphate cement($6.13mm{pm}2.07$) was smaller than former. 3) In Actinomyces viscosus, the diameter of inhibition zone to Zinc oxide eugenol cement($17.40mm{pm}5.20$) was largest and that to Vitapex($8.80mm{pm}1.70$) was next order. 4) In Fusobacterium nucleatum, the diameter of inhibition zone to Vitapex($42.33mm{pm}17.2$) was largest and those to Calcium hydroxide paste(Pulpdent Tempcanal)($14.47mm{pm}3.72$) and Zinc oxide eugenol cement($8.93mm{pm}2.71$), Zinc phosphate cement($8.20mm{pm}2.27$), Calcium hydroxide p..