A foxtail millet narrow spikelet mutant which was induced from Yugu1 by EMS treatment, was genetically identified and named as sins1. The mutant exhibited narrow-spikelet, low-plant-height, short-thin-panicle, short-narrow-leaf, low-spikelet-number per panicle, as well as low-1000-grain weight. Compared with its wild-type Yugu1, plant height, panicle length, panicle diameter, flag-leaf length, flag-leaf width, the 1000-grain weight, spikelet number per panicle of sins1 were decreased by 3.89 %, 17.41 %, 21.62 %, 15.07 %, 25.87 %, 41.09 %, 25 % respectively (P≤0.05). Genetic analysis suggested that its F1 hybrid plants were restored to wild type and 3:1 segregation ratio of wild type to mutant plants were observed in the F2 generation of sins1×Yugu1, suggesting that the narrow-spikelet trait of sins1 mutant is controlled by a single recessive nuclear gene. Genetic mapping of the mutant gene was conducted using narrow-spikelet individuals from the F2 segregating population of sins1×SSR41. Finally, the mutant gene was mapped into genomic region within SSR markers 3-2658 and CAAS3031 in chromosome 3, with a 7.709 Mb interval. This research had laid the foundation for fine-mapping of the narrow spikelet causal gene and will promote spikelet development related research in cereal crops.