The bacterium Bacillus licheniformis, which exhibits high hydrolytic activity toward arabinan, was isolated from soil, and its gene encoding endo-1,5-${alpha}$-L-arabinanase was cloned and sequenced. The gene has an open reading frame that encodes 328 amino acids, including a signal peptide of 37 amino acids. Endo-1,5-${alpha}$-L-arabinanase, a member of glycosyl hydrolase family 43, was expressed in Escherichia coli and purified as a 34-kD monomer with a specific activity of 27 U/mg. Optimal activity toward debranched arabinan (linear 1,5-${alpha}$-L-arabinan) occurred at pH 6.0 and $35^{circ}C$, with a $k_{cat}$ of 160/sec and a $K_m$ of 19 mg/mL.