Polysaccharide-degrading enzymes of the anaerobic rumen bacterium Ruminococcus flavefaciens strain 17 were exmined. This work demonstrated that R. flavefaciens strain 17 produces a complex array of enzymes active against cellulose, hemicellulose (xylan) and lignin. These enzymes are xylanase, avicellase, acid-swollen cellulase, carboxymethyl cellulase (CMCase), pNP-cellobiosidase (pNPC), pNP-glucopyranosidase (pNPG), pNP-xylopyranosidase (pNPX) and pNP-arabinofuranosidase (pNPA). Although R. flavefaciens, is an anaerobic bacterium, its enzymes worked optimally under aerobic conditions and with dithiothreitol (DTT), except in the case of pNP-xylopyranosidase. pNP-xylopyranosidase exhibited a higher level of activity under anaerobic conditions with DTT. It was demonstrated that the cross-links between arabinose side chains, which esterified via ferulic acid and p-coumaric acid, were cleaved by R. flavefaciens esterase and alpha -arabinofuranosidase.