5 serotypes(a, b, c, d, e) of Actinobacillus actinomycetemcomitans showed distinct hybridization patterns(DNA fingerprinting patterns) when the bacterial DNA were hybridized with randomly cloned 4.7-Kb sized DNA probe. The sizes of hybridized bands in each serotypes were different among serotypes and represented unique patterns of hybridization with the probe used. The serotype a showed two bands of fingerprinting patterns: 23.1 kb and 2.5 kb respectively. Serotype b and c showed single band: 6.6 kb and 9.5 kb, respectively. Serotype d and e showed two bands of hybridization: 23.1 kb and 2.8 kb, and 23.7 kb and 2.1 kb, respectively. The results indicate that this standard fingerpriting patterns of DNA hybridization with 4.7 kb probe can be further used for genotyping clinical isolates of Actinobacillus 8ctinomycetemcomitansand its relevance with periodontal disease activity.