Rice embryo contains valuable materials which are related to human health and industrial material, thus controlling embryo size is more and more important in the field of rice breeding. Especially, main health-aid components such as γ -aminobutyric acid (GABA), tocopherol and vitamins showed positive-correlation with embryo size. We obtained three enlarged embryo character mutants derived from Hwacheongbyeo (Korean japonica cultivar) by treatment of chemical mutagen, N-methyl-N-nitrosourea(MNU). These three mutants were named according to their embryo size as ge-m, ge, ge-s. The result of allelism test between Hwacheongbyeo, ge-m, ge and ge-s represented that the embryo size of ge and ge-s was controlled by the same gene(Giant embryo, GE). Through GE locus sequencing of three mutants, we found that each of ge and ge-s mutant has a point mutation, causing non synonymous amino acid substitution. On the other hand, ge-m mutant, the embryo of which featured intermediate size in between those of Hwacheongbyeo and ge, turned out to be non-allelic to the GE locus, suggesting it is likely a novel gene, which influences rice embryo development through a different mechanism than GE gene. Fine mapping of ge-m is currently in progress. This work was supported by a grant from the Next-Generation BioGreen 21 Program (Plant Molecular Breeding Center No. PJ008125), Rural Development Administration, Republic of Korea.