A rice floral mutant was obtained from a japonica variety Zhonghua 11, which was characterized with the phenotype of more stamens, more pistils and early flowering. Genetic analysis showed that the mutant phenotype was controlled by a single recessive gene, which was designed as floral organ number 5 (fon5). To map fon5, an F2 population was derived from the cross between Huajingxian 74 and fon5 mutant. Gene fon5 was roughly mapped between the microsatellite markers RM400 and RM412 on chromosome 6 with genetic distances of 10.5 and 1.6 cM, respectively. Then, six new po-lymorphic InDel markers were developed in the region. According to the physical information of the markers, locus fon5 was finally delimited to a region of 116 kb.