Self-incompatibility in crucifers is under the sporophytic control of a single locus, S. When identical S-alleles are expressed in both pollen grain and stigma papilla cell, pollen tube does not penetrate into the cell wall of papilla. S-glycoproteins(also called as SLGs) co-segregated with S-alleles are found in stigma and are most likely responsible for the recognition reaction of self-incompatibility. In Brassica campestris, the major morphological differences between the self-incompatible and self -compatible strains are only a few. We have analyzed the aspects of flower organs, SLGs, genetic factors between self-incompatible strain, S23 and self-compatible strain, C635. The dehiscent side of anthers faced toward the pistil at flowering time in C635, however, it was inverted in S23. The upper side of papilla cell in S23 was gapped each other, therefore, one pollen grain could often attach to two or more papilla cells, while that of papilla cell in C635 was flattened and closely contacted between them. By means of immunological analysis, we showed that self-compatible strain contained stigmatic SLGs that are expressed with a similar spacial and temporal pattern to that described for the SLGs of self-incompatible strains. And the SLGs segregate with the self-compatibility phenotype in F2 progeny. when the difference of genomic DNA constitution was examined by southern hybridization in C635, S23 and their F1 hybrid, the patterns of the gel blot clearly differentiated these three strains. From test-cross results, self-compatibility could be ascribed to the action of a modifier gene (Mod vs mod) which lies outside the S-locus. The recessive mod gene supresses the action of S-alles on the pistil but does not act on the pollen.