Radiation mutagenesis is available for crops germplasm creation. In this study, gamma-ray irradiation was used to induce the rice cultivar T98B which is a main maintainer line of hybrid rice, under the treatment of mature seeds at a dose of 300 Gy. It focused on screening and grouping of agronomic mutants, and the frequency for each type was also investigated. The results showed that, by contrast of T98B, the germination rate for M1 plants and M2 plants were both significantly suppressed, with a decrease of 22.35% and 14.67% respectively. In M2 population, 207 candidate mutants were screened. Of which, 168 were validated steadily inheritable via a phenotyping test from M3 to M5, accounting for a total mutation frequency of 0.673%. Furthermore, they were divided into 3 groups regarding leaf group, stem/tiller group and grain/flower group, according to the part that it occurred to mutate on. Each group above included 34, 37 and 97 mutants respectively, representing a ratio of 20.24%, 20.02% and 57.74%. The common mutants were the ones varied on fertility, leaf color and plant height, and it presented a mutation frequency of 0.212%,0.092% and 0.088% respectively. Moreover, a brief description on the phenotypes for each group was provided. The results indicated that, agronomic mutants in rice could be effectively obtained via gamma-ray irradiation, and several mutants gained here would be severed as useful germ resources for advancing the work on rice genetic improvement.