Japonica line 02428, possessing wide compatibility gene S-5n, showed semi-sterility as crossed with indica variety IR24. Genetic analysis was conducted on the spikelet fertility in segregation generations from the crosses of 02428 with IR24, Pecos and Akihikara. The results indicated that the sterility in hybrids between 02428 and IR24 was controlled by a single non-allelic to S-5 gene and its inheritance fitted to one-locus sporo-gametophytic interaction model. Pecos, an American variety, has a neutral allele. The new sterility locus was preliminarily located near G24 marker on chromosome 11 detected by RFLP. The non-allelic S-locus in the study is named tentatively S-p(t). It was found that the sterility caused by the cross of Akihikara and IR24 was controlled by two S-loci, S-5 and S-p(t), and its genetical effect was additive.