Abstract: Aeromonas caviae W-61 produces multiple extracellular xylanases, the xylanases 1, 2, 3, 4, and 5. In this study, we purified and characterized the xylanase-4 gene of A. caviae W-61, and cloned it. The purified xylanase-4 consisted of a single polypeptide with molecular masses of 120 kDa. The xylanases 4 was endo- -1,4-xylanase with optimum temperature 40°C, optimum pH 6.0 and temperature stability 40-50°C. Various xylo-oligosaccharides such as xylobiose, xylotriose, xylotetraose, xylopentaose and xylohexaose were formed, and a small amount of xylose was detected as the hydrolysis products. The N-terminal amino acid sequence and several identical internal amino acid sequences of xylanases-4 were determined. From the sequence, 1.8 kbp xyn 4 was amplified by PCR and was cloned from the genomic DNA of A. caviae W-61. The flanking region of xylanase-4 were sequenced and it contained a sequence corresponding a typical signal peptide consisting of 27 amino acid residues at the 5` end. Putative promotor ( 35 and 10) sequences and a typical ribosome-binding sequence were present upstream the xyn 4.