Low yield per unit is a disadvantage character of mung bean industry in China. The identification of male sterility lines is crucial for harnessing heterosis, which can substantially increase yield. In this study, we identified a male sterile mutant, ms2 (male sterile 2) from the EMS mutant library of Zhonglü5 (ZL5). During the vegetative growth stage, ms2 exhibited no significant phenotypic differences compared to the wild-type ZL5. Although the floral organs of ms2 developed normally, the stamen abortion resulted in a stay-green phenotype of ms2. Genetic analysis revealed that the sterility of ms2 is controlled by a single recessive nuclear gene. The F2 population derived from the cross between ms2 and Wankelü3 (WK3) was used as the mapping population. MS2 was mapped within a 66.7 kb interval flanked by markers M5 and M8 on chromosome 6, containing six annotated genes. Sequence analysis of these genes revealed two base transitions in the second and third introns of the glutamine synthetase gene (Vradi06g05640) in ms2. Expression analysis indicated that the expression level of this gene in ms2 was significantly lower than in ZL5, suggesting that Vradi06g05640 is likely the candidate gene for ms2. In summary, our study provides valuable insights into the mechanism of male sterility and the utilization of heterosis in mung bean.