Research on tongil-type rice has aimed to enhance genetic diversity and yield through indica-japonica hybridization; however, poor eating quality remains a limitation in Korea. We evaluated three high-yielding tongil-type waxy cultivars, focusing on the allelic variation in the granule-bound starch synthase I (GBSSI) gene and its effects on quality traits. Physicochemical properties, including texture and retrogradation, were assessed using a texture analyzer, and pasting properties were analyzed using a Rapid Visco Analyzer (RVA). ‘Hanareumchal’ showed the softest texture (1.70 Kgf) and the slowest retrogradation rate. Genetic analysis revealed a unique Wx-g2 allele derived from Japanese waxy rice (‘Odorokimochi’), which likely underlies these favorable traits. RVA profiling further indicated reduced viscosity parameters, supporting its suitability for processed rice products that require extended shelf life and texture stability. These findings highlight the role of Wx-g2 in improving tongil-type waxy rice and provide useful insights for breeding programs targeting enhanced processing performance.