Catechol 2, 3-dioxygenase (C230) catalyses the oxidative ring cleavage of catechol to 2-hydroxymuconic semialdehyde. This is one of the key reactions in the metabolism of the widespresd pollutant aniline. We have cloned a gene encoding C230 from cells of the aniline degrading bacteria, Pseudomonas acidovorance KCTC2494 strain and expressed in E. coli, A 11.3-kilobase Sau3A partial digested DNA fragment from KCTC2494 was cloned into phagemid vector pBluescript and designated as pLP201. The C230 gene was mapped to a 2.8-kb region, and the derection of transcription was determined. The cloned C230 gene contains its own promoter which can be recognized and employed by E. coli transcriptional apparatus. C230 activities of subclones were identified by enzyme assay and activity staining. The T7 RNA promoter/polymerase system and maxicell analysis showed that a polypeptide with Mw of 35 kDa is the C230 gene product.