An endo-(l→4)-β-D-xylanase from a cellulase-free Chainia strain was substantially purified and subjected to amino acid sequencing. The first forty N-terminal amino acid residues show high homology with endo-xylanases from Bacillus pumilus, B. subtilis, B. circulans, andSchizophylum commune, less homology with endo-xylanases from Aureobasidium sp. andPseudomonas fluorescens, and slight homology, but including a possible catalytic Asp residue, with catalytic domains of endo-xylanases from Clostridium thermocellum,Cryptococcus albidus, and an alkalophilic Bacillus and with a cellobiohydrolase fromCellulomonas fimi. The enzyme attacks substrates as small as xylotetraose and has xylosyltransferase activity. It is most active at pH 6 and 60°C and most stable between pHs 5 and 7.