The role of phenolic acids on sorghum and maize hardness was evaluated among eight cultivars of each of the cereals representing hard and soft classes. Bran and flour fractions were evaluated for monomeric and diferulic phenolic acids using high performance liquid chromatographic and mass spectrometric (LC–MS/MS) techniques. Bran samples of harder grains had more phenolic acids than those of soft types. Intra-class testing showed slight differences in cultivars within the hard and soft classes. The content of phenolic acids was a useful indicator of hardness distinguishing between hard and soft maize and sorghum cultivars. Correlation coefficients between monomeric acids of maize bran, mostly ferulic acid, and grain hardness were higher than those of sorghum. Maize bran ferulic acid content was strongly correlated with Tangential Abrasive Dehulling Device (TADD) hardness (r = - 0.776, p < 0.001). This study is the first to show that there is a relationship between bran phenolic acid content and sorghum and maize hardness.