Abstract: In Brassica, self-incompatibility was controlled sporophytically by a single, complex S-locus: a complex region with multigenes, so-called S multigene family. Most members of S-multigene family dispersed in Brassica genome. About 100 S-alleles were identified and their differentiation spanned about 10 million years. Three types of genes were identified on S-locus:SRK,SLG and SCR /SP11；SRK and SLG express in stigma and SCR/SP11 in pollen. SRK protein plays the key function in recognization of self-pollen and SLG enhances this function. In all S alleles, SLG and S-domain of SRK has very high DNA sequence similarity: 85%～98%, in the same S-allele. Gene conversion may be the reason of maintainance of high level homology between SLG and SRK.SRK,SLG and SCR linked together in physical map and these genes exhibited high diversity in sequences. Physical distance was about 20～25 kb between SLG and SRK. In Brassica, codominant relationships are more frequent than dominant and recessive ones in both the stigma and the pollen, as one characteristic of SI in Brassica. There were two hypotheses about evolutionary models of SI: two-gene model and neutral-variant model. It may be that several different mechanisms contribute to the evolution of new S-allele specificities in natural populations.