The mutant population of Xanthomonas oryzae pv oryzae strain differential to rice bacterial blight resistance gene Xa23 has been constructed mediated by transposon in vivo . The results of PCR amplification with specific primers and analysis of flanking sequence of mutants indicated that the foreign DNA has been integrated into X. oryzae pv oryzae genome. Four mutants with changed avirulent activity to Xa23 gene have been identified by artificial inoculation. It is possible to clone genes that are required for AvrXa23 avirulence activity using this new strategy.