The butanol-producing Clostridium saccharoperbutylacetonicum strain N1-4 abundantly secreted xylanase into the culture supernatant when cultured on delignified rice straw. The xylanase signal peptide was identified based on its N-terminal amino acid sequence and was presumed to be secreted by the Sec-system. The presence of xylanase in the medium indicated that the strain was capable of utilizing xylan as a substrate. Also, butanol production obtained using a medium supplemented with xylan was comparable to that obtained using the same strain cultured on a medium supplemented with glucose. The signal peptide facilitated the secretion of exogenous cellulases expressed by butanol-producing strains and promoted butanol production from dignified rice straw.