The xantho-oligosaccharides with different ratio of the viscosity to the reducing sugar were produced from xanthan by Cellulomonas sp. LX. It was found that the cell growth of Xanthomonas campestris pv. campestris could be inhibited by some types of the xantho-oligosaccharides and the significant inhibitory activity was observed when S4 and S5 were tested, in which the values of the viscosity/reducing sugar were 232.5 and 101.4, respectively. The xantho-oligosaccharides not only inhibited the growth of X. campestris pv. campestris but also reduced the production of xanthan which is the virulence of X. campestris pv. campestris. The production of the extracellular enzymes released from X. campestris pv. campestris including cellulase, chitinase, pectinase and proteinase also were partially inhibited. The study indicated the potential application of the xantho-oligosaccharides in the management of diseases caused by X. campestris pv. campestris in several important crop plants. (c) 2006 Elsevier Ltd. All rights reserved.