Abstract A group of regulatory factors containing the MADS box domain is playing an important role in controlling floral organ induction and development. In this study, we have isolated and characterized two cDNA clones from rice, OsMADS2 and OsMADS4, which encode MADS-domain containing proteins. The OsMADS2 amino acid sequence shows more than 50% identity to GLO of Antirrhinum majus, PI of Arabidopsis, and GLO PI homologs of petunia and tobacco. Also, these two rice proteins contain, in addition to the conserved MADS box sequence, two other conserved sequences in the same locations as are found specifically in the GLO PI family. RNA blot analysis showed that the rice MADS box containing genes were expressed throughtout flower development. While OsMADS2 expression increased strongly as the flower matured, OsMADS4 expression was at a higher level from early stages of flower development. RNA blot hybridization with total RNA from each floral organ showed that the expression of these genes was restricted to anther and carpel. In situ hybridization studies indicated that the transcripts were present mainly in pollen, tapetum and also in stigma. Since rice flowers consist of a single perianth which resembles sepal, GLO PI homologs in rice would be expected to be expressed predominantly in reproductive organs. These results suggest that the rice OsMADS genes may be members of the GLO PI family.