Leaf color is usually determined by the number, structure, and photosynthetic characters of the chloroplast. Isolation of the functional genes in leaf discoloration mutants of the C4 model plant foxtail millet and deciphering their functions is a way to disclose the regulation mechanism of C4 plant chloroplast biogenesis, development and photosynthesis. In this study, a stripe-leaf mutant t122 was identified from the EMS-induced mutant library of the foxtail millet variety Yugu1. The mutant t122 was observed with developmental retardation, and irregular white stripes on leaves. In contrast to the wild type, the significant decrease on the plant height, leaf length, leaf width, main panicle diameter, main panicle weight, and seed setting rate was observed in t122 mutant, whereas an increase on the panicle number per plant was detected. The photosynthetic capacity of t122 was impaired. By the leaf anatomy analysis, no significant difference in the distance between leaf veins, the number of cell layers between vascular bundles, and the cross-sectional cell area of leaves was observed in t122; however, an increased on the leaf cell length was detected. The ultrastructural observation of chloroplasts showed that, in t122 the chloroplasts showing functional structure were only detected in subsets of leaf cells. The segregation analysis suggested that the stripe-leaf trait of t122 was controlled by a single recessive nuclei-encoding gene. Using the method of MutMap, the candidate gene was mapped to the region of 24.0 Mb - 30.0 Mb on chromosome 3. Collectively, these results laid a good foundation for future cloning and functional characterization of the stripe-leaf gene in foxtail millet.