Abstract: Seeds of several indica rice cultivars were treated by nucleus irradiation and strains with giant embryo(ge) were selected in M2 and M3 generation. The inheritance of giant embryo character in rice was studied by investigating the size of embryo of plants in generations of P1、P2、F1、F2 and BC1F1, which were made by crossing the giant embryo mutants 98-14geB and Mge86 with their corresponding original types.The main results were as following: The giant embryo mutation frequency in M2 averaged 0.00125%, at range of 0.00029%-0.00285%. The giant embryo mutation frequency in M1 averaged 0.03015% or 0.03911%, depend on the different calculation methods. The ge mutants were detected in 9 M2 populations of 11 induced varieties. Mutation frequency varied with applied dosage and mutated materials. The trait of giant embryo is genetically controlled by a pair of recessive genes. The size of rice embryo is only controlled by the genotype of zygote, and not affected by the genotypes of the female parent plant and the cytoplasm. Hence, it is possible to identify giant embryo mutants directly from seeds of M2 or F2.. Population allelic tests shown that the gene in TgeB、1813geB、98-14geB and Mge86 are allelic to the ge gene of Japonica mutant “1137”.