Oxidants such as hydrogen peroxide (H₂O₂) and superoxide anion (O₂) is dangerous in cells and tissues under physiological condition. Catalase is a hemoprotein that is ubiquitously present in aerobic and aerotolerent cells containg a cytochrome system and decomposes the peroxide into water and molecular oxygen. Gram-negative bacterium Vitreoscilla, a member of the Beggiatoa family, is an abligate aerobe and produce hemoglobin. The presence of catalase in these cells could present the accumulation of peroxide, thus protecting the cells from self destruction when the oxygen concentration is high. To identify Vitreoscilla catalase gene, Southern hybridization containing Vitreoscilla genomic DNA fragment was performed using a oulionucleotide probe. Also Vitreoscilla genomic library constructed 20∼25 kb fragments of digested Vitreoscilla genomic DNA using broadhost-range cosmid vector pVK102 with Escherichia coli Le392 as a host. Since pVK102 is sensitive kanamycin and is resistant tetracycline, these transformants containing recombinant vectors was selected using antibiotics. These transformants were screened by colony hybridization. We identified catalase gene of Vitreoscilla by Southern and colony hybridization.