The determination of the atomic configuration of metallic glasses is a long-standing problem in materials science and solid-state physics(1,2). So far, only average structural information derived from diffraction and spectroscopic methods has been obtained. Although various atomic models have been proposed in the past fifty years(3-8), a direct observation of the local atomic structure in disordered materials has not been achieved. Here we report local atomic configurations of a metallic glass investigated by nanobeam electron diffraction combined with ab initio molecular dynamics simulation. Distinct diffraction patterns from individual atomic clusters and their assemblies, which have been theoretically predicted as short- and medium-range order(6-8), can be experimentally observed. This study provides compelling evidence of the local atomic order in the disordered material and has important implications in understanding the atomic mechanisms of metallic-glass formation and properties.