In rice breeding, genes for seed dormanoy as well as the markers for each of them are required of an incorporation of an adequate seed domancy into japonica cultivrs To screen genetic Ioci for seed dormancy in rice (Orvza saliva L.), two kinds of populations were tested: (i)an Fz population of a hybrid Milyang 23 I Todorokiwase. and (fi) Fl populations from a three-way cross, in which an indica donor of strong dormancy, IR 36, was crossed with non-dormant japonica cultivars, Nekken 2 and Miyukimochi, in the form of IR 36/ Nekken 2// Miyukimochi. The seeds predated on the F2 plants from the single cross and those on FI plants from the three-way cross were tested at three times: immediately after maturation, after 60 d storage at 4C, and after breaking dormancy (7 d at 50C). Of 24 marker Ioci assayed, at least fore loci linked to seed dormancy were detected. The strong seed dormancy of Milyang 23 was linked with three isozyme genes: Pgi-I1 on chrompsome 3, Amp-32 on chromosome 6, and Est92 on chrmosome 7, while the strong seed dormancy of IR 36 was linked with C+ (apiculus color) on chromosome 6, Est-92 on Chromosome 7, and Acp-21 an chromosome 12. The high level of seed dorloci. Differential responses of inch Iocl to a dormacy-breaking treatment were detected. An allele from IR 36 at a locus on chromosome 6 seemed to be responsible for strong seed dormany after maturation and to be easliy broken during storage. This allele may be incorporated into japonica ries by means of marker C for apiculus color.