Screening of dwarf mutants plays an important role in understanding of the molecular mechanism in rice plant architecture. We report here the identification and characterization of a novel rice dwarf mutant from tissue culture progeny of a Japonica variety Kitaake, dm. The mutant shows a pleiotropic phenotype, including dwarf, fragile stem, low fertility and decreased 1000-grain weight. By using F2 and its following segregated populations, we narrowed down dm gene into a 168 Kb region on the long arm of chromosome 4. Our results indicate that DM represents a new locus responsible for rice plant architecture.