Abstract: Grain shape is a key trait governing rice yield and quality. A 15-base sequence（5’-tccttcaccaagga-3’）in the boundary region of the last exon of the GW3p6 gene mutates to a 13-base sequence（5’-agtatatatacat-3’）, leading to alterations in intron splicing sites. This mutation results in slender grain shape, thereby improving rice quality and yield. To facilitate the application of GW3p6 in rice yield and quality breeding, this study developed an efficient and low-cost functional marker for GW3p6 based on melting temperature（Tm）detection. Primers were designed adjacent to the variation site of GW3p6, and genotypes were distinguished by Tm analysis using a QuantStudio™ 3 quantitative PCR instrument. The marker was used to detect 94 self-crossed progenies of a residual heterozygote from the recombinant inbred lines of Shuhui 527 and Mianhui 437. The Tm values of the two alleles were 74.33°C and 71.16°C, respectively, enabling clear discrimination of three genotypes, which fully matched the phenotypic traits. The GW3p6 functional marker developed in this study combines the advantages of high-resolution melting（HRM）-based molecular markers（high efficiency and low cost）while reducing equipment requirements for Tm detection, thus facilitating genotyping of this gene and its application in breeding programs. Grain shape is a key agronomic trait controlling rice yield and quality. A sequence variation in the last exon boundary region of the GW3p6 gene was identified, where a 15-bp sequence（5'-tccttcaccaagga-3'）was mutated to a 13-bp sequence（5'-agtatatatacat-3'）. This mutation altered the intron splicing site, resulting in slender rice grains and improved grain quality and yield. To facilitate the application of the GW3p6 gene in rice breeding for high yield and quality, a high-efficiency and low-cost functional molecular marker based on melting temperature（Tm）analysis was developed. By designing primers flanking the mutation site and utilizing the melting temperature analysis function of the QuantStudio™ 3 quantitative PCR instrument, the GW3p6 genotypes of 96 rice samples were detected. The results showed that the two homozygous alleles exhibited distinct melting temperatures of 74.33℃ and 71.16℃, respectively, while the heterozygous genotype displayed two non-overlapping melting peaks, enabling accurate identification of the three genotypes. The development of the marker will promote the application of the GW3p6 gene in rice breeding.