The indica rice Xieqingzao eB1 (XQZ eB1), a mutant with an elongated uppermost internode, was produced by mutagenesis from elite maintainer line Xieqingzao B (XQZ B) using γ-radiation. Compared with the wild-type XQZ B, plant height and the length of the rice panicle neck, second internode and third internode from the panicle were elongated significantly in XQZ eB1. Genetic analysis indicated that the trait for uppermost internode elongation of XQZ eB1 is controlled by a single recessive gene eui1, which is allelic to that of IR50eui (derived from 76:4512). Further studies were carried out using the bulk segregated analysis approach. An F3 population, derived from the cross XQZ eB1×Aijiaonante, was used to map the mutant gene eui1. Two SSR makers, RM164 and AC9, were identified to link to eui1, their genetic distances to eui1 being 18.4 and 7.9 cM, respectively. The eui1 gene was also mapped to the long arm of chromosome 5 in this research.