The purpose of the study was to identify the characteristics of the pathogenic microorganism Actinobacillus actinorayceteracomitans. The experiments of this study consist of the decision of existence or nonexistence of Actinobacillus actinorayceterncoraitans in the air of dental clinics, the effect of sugar on the growth of Actinobacillus actinorayceteracoraitans, and the sensitivity of Actinobacillus actinoraycetemcoraitans to Fluorine and antibiotics. The results of the experiments are as follows. 1. Actinobaeillus actinornyceteracornitans did not exist in the air of 4 dental clinics in Seoul 2. The growth of Actinobacillus actinornycetemcornitans in the media containing glucose or sucrose was faster than in the media without these, and glucose was more effective than sucrose. 3. Actinobacillus actinomyceteracoraitans was not susceptible to Fluorine at concentration between 0 ppm and 300 ppm. 4. Order of sensitivity of Actinobacillus actinomycetemcomitans to antobiotics was as follows: Tetracycline > Kanamycin > Ampicillin.