This report demonstrates the presence of S - RNases in style of self - incompatible Japanese plum (Prunus salicina Lindl.) and presents information about cDNA sequences encoding the S - RNases. Two stylar glycoprotein spots that were found in highly basic zone of 2D - PAGE gel with Mr of about 30 kDa shared similarity in N - terminal amino acid sequence and immunological characteristics with other rosaceous S - RNases and appeared to be S - RNases of Japanese plum. Deduced amino acid sequences from the cDNA clones encoding these glycoproteins contained two active sites of T2/S type RNases and five regions conserved among other rosaceous S - RNases. Genomic DNA blot and RNA blot analyses using the cDNA clones as probes and phylogenetic analysis based on the deduced amino acid sequences from the cDNAs all indicated that the cDNA clones encoded S - RNase corresponding to the stylar glycoproteins detected on 2D - PAGE gel. Phylogenetic analysis based on the deduced amino acid sequences from the cDNAs supported the hypothesis that the S - RNases of Rosaceae have diverged after the divergence of subfamilies but before the divergence of species.