Present study is aimed to experimentally scrutinize the horizontal distribution of vertical stress underneath granular silos using a high-sensitivity stress sensor mat system. Two granular materials of contrasting particle shape but similar size were utilized to construct granular silos by the alleged local source method. The experimental results indicate that the average vertical stress is agreeable with the value predicted by Janssen's law; however, the distribution of measured vertical stress is found to be non-uniform over the horizontal plane, which is contrary to the assumption of Janssen's law. The distribution non-uniformity is aggravated by a more elongated particle shape. The maximum vertical stresses occur at vicinity of enclosing wall and the vertical stresses lower than the average value appear at the center zone with fluctuations. We proposed an empirical equation with three parameters for characterizing the distribution of vertical stresses normalized by the average value given by the Janssen's law. (C) 2020 Elsevier B.V. All rights reserved.