A gene encoding an endoxylanase of Bacillus sp. was cloned acid expressed in Escherichia coli. The entire nucleotide sequence of a 1,620 bp SmaI fragment containing the endoxylanase gene was determined. The endoxylanase gene was 639 bp long and encoded 213 amino acids which showed up to 96% amino acid homology with other endoxylanases. The encloxylanase produced by E. coli harboring pKJX4 was purified by ion-exchange chromatography (DE-52 and CM-Si) and its N-terminal sequence was determined to be Ala-Gly-Thr-Asp-Tyr-Trp-Gln-Asn-Trp-Thr-Asp-Gly-Gly-Gly-Thr. The endoxylanase expressed in E. coli was identical to that of the riginal Bacillus sp, whose molecular weight was approximately 20,400. Most of the produced endoxylanase was localized in the periplasmic space of E. coli. When the endoxylanase was reacted with 2% oat spelts xylan (w/v) at 40 degrees C for 10 h, the major product was xylobiose which is known to be a selective growth stimulant to one of the healthy intestinal microflora, Bifidobacteria.