Abstract: The mutants, which produced brown leaf midribs, reduced the content of lignin by 40% to 60% compared with normal varieties. This low lignin content largely promoted the rate of digestion in livestock. The F₂ population was constructed from the hybrid of N592 (bmr-6) and Sa (white midrib) to map the bmr-6 gene. The ratio of white and brown midribs was 3 to 1 in the F₂ population. Therefore, the bmr-6 gene is a single recessive gene. Using 171 SSR markers and F₂ recessive population, one SSR (simple sequence repeats) marker (txp295) that linked with the bmr-6 gene was detected and the genetic distance was 4.2 cM. In addition, the bmr-6 gene was mapped to the seventh linkage group of sorghum because the txp295 marker was located on this linkage group.