Xanthomonas oryzae pv. oryzae causes bacterial blight in rice (Oryza sativa L.). The effect of a mutation in the wxoD gene, that encodes a putative O-antigen acetylase, on xanthan production as well as bacterial chemotaxis was investigated. The mutation increased xanthan production by 52 %. The mutant strain was non-motile on semi-solid agar swarm plates. In addition, several genes involved in chemotaxis, including the cheW, cheV, cheR, and cheD genes, were down-regulated by a mutation in the wxoD gene. Thus, the mutation in the wxoD gene affects xanthan production as well as bacterial chemotaxis. However, the wxoD gene is not essential for the virulence of X. oryzae.