A rice semidwarf and deformed flower mutant, temporarily named as sddf3, was identified from ⁶⁰Co γray radiation mutation in japonica rice variety Nipponbare. The mutant was characterized by semidwarf, more tillers, semienclosed panicle, stamens dysplasia and nonpollen. Genetics analysis indicated that the mutant was controlled by a single recessive gene. The F₂ mapping population was derived from a cross between the heterozygous sddf3 genotype and a wide compatible variety Dular. The gene was located in a 227 kb region between the In/Del marker 333591 and 333818 on chromosome 3 in rice, which was assumed to be a new gene controlling semidwarf and deformed flower.