Plant mitogenactivated protein kinases (MAPKs) have been implicated in plant defense as a new component of the defense signaling pathways.In this study,a Sclerotinia sclerotiorum cDNA clone in Brassica campestris ssp.chinensis cv.Duanbaigeng was isolated and characterized.The gene was designated as BcMPK4 (DDBJ accession number AB557751),which contains 1 334 bp nucleotide and encodes 373 amino acids.BcMPK4 had different homology score of amino acid compared with MPK4 genes of other plants.Phylogenetic analysis revealed the evolutionary conservation of these proteins among diverse species.Southern blotting hybridization with genomic DNA showed that BcMPK4 belonged to a multigene family.Realtime quantitative PCR analysis revealed that BcMPK4 transcript was increased after inoculated with S.sclerotiorum.Expression characterization of BcMPK4 in Brassica campestris ssp.chinensis indicated that it might be involved in host resistance against S.sclerotiorum.