A xylanase gene, xynF1, was cloned and characterized from a shoyu koji mould Aspergillus oryzae KBN616. The xynF1 gene was found to be comprised of 1484 bp with ten introns. The deduced amino acid sequence encodes a protein consisting of 327 amino acids (35,402 Da) which is very similar to the fungal family F xylanases such as Aspergillus nidulans XlnC, Aspergillus kawachii XynA and Penicillium chrysogenum Xy1P. The intron/exon organization of xynF1 is very similar to that of the fungal family F xylanase genes. Plasmid pXPR64, which contains 64 copies of the xynF1 promoter region (PxynF1) in the same direction, was constructed and introduced into A. oryzae. This led to reduced expression of both xylanase and beta-xylosidase genes in the transformants.