Mutants on stalk strength are essential materials for the studies on the formation of plant cell wall. In this study, a brittle stalk mutant of maize, designated as Bk-x, was screened from a Mutator inserted mutant library. At the germination and early seedling stage, the mutant plants were indistinguishable from the normal ones. However, all of the plant organs were brittle after the 5th-leaf stage and remained brittle throughout the rest of the growing period. Microstructure observation showed that the cell wall in vascular bundle sheath of Bk-x was thinner than that in normal plants. The leaf mechanical strength in Bk-x was 77.9%of that in normal plants growing at Xishuangbanna (BN), Yunnan province and that was 61.7%in Wuhan (WH), Hubei Province, China. The proportion of cellulose was 12.3%in Bk-x, which was significantly lower than that in normal plants (26.7%), while the soluble sugar content was 36.1%in Bk-x, which is significantly higher than that in normal plants (12.4%). Genetic analysis using two F2 populations and one F2:3 families demonstrated that the trait of brittle stalk is controlled by a single recessive gene.