Involvement of the S'-haplotype in self-compatibility in the Japanese plum cultivars 'Santa Rosa' ((SSe)-S-c) and 'Beauty' ((SSe)-S-c), was investigated. Self-pollination and pollen-tube growth tests confirmed that cv. 'Rio', which also has a S-e-haplotype ((SSe)-S-a), is self-compatible. In self- and cross-pollination experiments between cultivars with the (SSe)-S-c haplotype, the resultant progenies segregated into two S-haplotypes, (SSe)-S-c and S'S', suggesting that only the S-e-haplotype was inherited in progeny from the male parent. These results indicated that the S-e-haplotype is responsible for self-compatibility. Expression analyses of S-RNase showed that the S-e-RNase gene was transcribed in the style. Therefore, it appeared that inhibition of transcription of the S-e-RNase gene is not responsible for the self-compatibility in the S-e-haplotype of Japanese plum.