Objective As an important component of rice plant architecture， tiller angle has a complex genetic foundation. More mutants and genes associated with tiller angle need to be identified to further elucidate the molecular mechanisms of tiller angle in rice.Method A rice spreading-grown mutant， tentatively named sg518 （spreading-grown mutant 518）， was obtained through ⁶⁰Co radiation mutagenesis to the local japonica rice variety Qiao-Gang Pearl Rice in Guizhou Province. Phenotypic identification， genetic analysis， gene mapping and candidate gene sequencing were conducted on this mutant.Result （1）Field traits showed that the mutant sg518 displayed a spreading-grown phenotype with a significantly increased tiller angle， along with a higher number of primary branches， increased grains per panicle， reduced grain size， and lower 1 000 grain weight compared to the wild type. （2）Genetic analysis indicated that the spreading-grown phenotype in the sg518 mutant was controlled by a single recessive nuclear gene. （3）Fine mapping revealed that the target gene was situated in an 88.7 kb region between RM287 and J1 on the long arm of chromosome 11. （4）MutMap analysis indicated a single InDel mutation with a SNP index of 1 was located on LAZY1 gene within this region. （5）PCR amplification and sequencing verified a 1 bp deletion in exon 3 of LAZY1 gene in the sg518 mutant， leading to premature termination of protein translation. Therefore， it was inferred that LAZY1 gene was the candidate gene for the sg518 mutant.Conclusion sg518 is a novel allelic mutant of LAZY1 gene， providing a theoretical foundation for further exploration into the function of this gene and the regulatory mechanisms of tiller angle in rice.