Acinetobacter calcoaceticus-Acinetobacter baumannii (A. calcoaceticus-A. baumannii) complex, which includes A. calcoaceticus (genospecies 1), A. baumannii (genospecies 2), Acinetobacter genospecies 3 and 13, has been identified as A. baumannii by automated bacteria identification system. The purpose of this study is to develop rapid genospecies classification of A. calcoaceticus-A. baumannii complex by molecular techniques. Random amplified polymorphic DNA (RAPD) and restriction fragment length polymorphism (RFLP) were determined for 4 reference strains and 80 isolates of A. calcoaceticus-A. baumannii complex from clinical sources. Four and eleven RAPD patterns were observed among the reference strains and the isolates, respectively. RAPD might be useful for genomic typing but not for genospecies classification of Acinetobacter spp. RFLP of 16S-23S rRNA intergenic spacer gene with three selected restriction enzymes (ApaLI, SwaI, and SalI) showed only four RFLP patterns in the reference and the isolates. Of 80 isolates, 10 of A. calcoaceticus (12.5%), 50 of A. baumannii (62.5%), 11 of A. genospecies 3 (13.75%), and 9 of A. genospecies 13 (11.25%) were classified by RFLP. This result suggests that RFLP of 16S-23S rRNA intergenic spacer gene of Acalcoaceticus-A. baumannii complex might be useful for genospecies classification.