The development of molecular genetic maps has accelerated the identification and mapping of genomic regions controlling quantitative trait loci(QTL) in rice (Oryza sativa L.). Minimizing embryo size in rice would increase proportion of edible endosperm.This study was conducted to determine the genetic basis controlling embryo size of rice grains in a recombinant inbred (RI) population derived from cross of a japonica cultivar,Asominori,with an indica cultivar,IR24,by means of 289 restriction fragment length polymorphism (PFLP)markers.Two parameters,embryo length and embryo width,which represent embryo size in rice,were estimated for each RI line and their parental varieties.Continuous distributions and transgressive segregations of embryo length and embryo width in rice were observed in the RI population,suggesting that embryo size was quantitative in grains of conventional varieties.Three QTL for embryo length were detected on chromosomes 1, 2, and 3 explained 17.9, 25.7, and 9.2%, respectively, of the total phenotypic variation. Three QTL for the embryo width were observed on chromosome 2, 8, and 10 and accounted for 13.5, 15.7, and 15.0% of total phenotypic variation, respectively. In addition, alleles with increasing and decreasing effects were detected from the both parents. The results and the tightly linked molecular markers that flank the QTL will be useful in breeding for embryo improvement in rice.