A bacterium exhibiting extraordinarily high catalase activity was isolated from a drain pool of a fish product processing plant that uses H2O2 as a bleaching and microbicidal agent. The isolate was a gram-negative, rod-shaped, oxidase-positive, facultative anaerobe capable of both fermentative and respiratory metabolism, and sensitive to vibriostatic compound O/129. Although the isolate was non-flagellated, its taxonomic characteristics and phylogenetic position based on a 16S rRNA analysis indicated that it belonged to the genus Vibrio. A culture medium containing living cells and a cell-free extract prepared from 48-h cultured cells of the isolate exhibited catalase activity of 680 units/mg cells and 7276 units/mg protein, respectively. The activity of the cell-free extract of the isolate was 2 orders greater than those of Escherichia coli and Bacillus subtilis. Application of the newly isolated bacterium or its enzyme will provide an effective means of decomposing H2O2 contained in industrial waste such as that produced in the paper, food, textile, and semiconductor industries.