Abstract: Field experiments were conducted at Jiangxi Agricultural University to study the genotype difference of seed nitrogen content in 412 indica rice,63 japonica rice,and 82 indica hybrid rice varieties.The results showed that the seed nitrogen content of cultivated rice had a significant genotype difference,with the range from 0.85% to 2.55%,and an average of 1.39%.The average seed N content of indica hybrid rice was 1.46%,which was significantly higher than that of japonica normal rice (1.39%) and indica normal rice (1.38%),and there was no significant difference between indica and japonica normal rice.The frequency distribution of seed N content exhibited normal curve,but the centers of frequency distribution were different among three rice types.The ranges of the cumulated frequency from 25% to 75% were 1.21%-1.52%,1.21%-1.51% and 1.36%-1.53% for indica,japonica,and indica hybrid rice,respectively.Ducan's Mutiple Range test showed that the maximum derivation of N content among indica hybridrice varieties was significantly lower than that among indica and japonica rice,which indicated that the seed N content of indica hybrid rice was more concentrated than that of indica rice and japonica rice.The maximum derivation within different cultivated rice types was very large.Thus,each rice type could be classified into several groups,and the difference between groups was significant.