The rice mutants of OsEMF2b inserted by T-DNA were studied cytologically.The results showed that the morphology and quantities of floral organ in heterozygous rice mutants were altered but the development of anther and ovule was not changed.The fertility of pollen and embryo sac of mutants was normal.Abnormities including non-dividing zygote,delayed embryo,abnormal embryo and syncytial with no cellularization,as well as the dissolution and degeneration of endosperm cell occurred during the development of seed.These abnormities resulted in the decrease of seed setting rate.The study indicated that OsEMF2b played an important role in the development of rice floral and seed.