A small-panicle mutant si-sp1 induced by chemistry (EMS) mutagenesis was isolated. The mutant exhibits small-panicle trait, as well as low-plant-height, low-spike-number per panicle and less-roots. Compare with its wild-type Yugu1, panicle length, plant height, spike weight per plant and spike number per panicle of si-sp1 were decreased by 37.8%, 9.0%, 40.3%, 31.7%, respectively, while the 1000-grain weight was increased by 20.2%. Genetic analysis showed that the small-panicle trait of si-sp1 mutant was controlled by one recessive nuclear gene. Genetic mapping of the mutant gene was conducted using small-panicle individuals from the F2 segregating population of si-sp1/Liaogu1. Finally, the mutant gene was mapped into genomic region within SSR markers CAAS8003 and SSR1038 in chromosome 8, with physical distances of 11.02 M. This research has laid the foundation for fine-mapping of the small panicle mutant gene.