Unlike crystalline materials, metallic glasses usually have a uniform structure without long-range periodicity and characteristic structural constituents. It has long been believed that no interfaces associated with separate grains can be found in metallic glasses. Here, we report on the successful synthesis of a gold-based nanograined metallic glass (NGMG) exhibiting a heterogeneously granular structure but possessing a glassy nature. The smallest particle size of the NGMG can be less than 10nm. Having the advantage of the high surface area typical for nanostructures, the Au-based NGMG shows significantly enhanced catalytic activity. In addition, this NGMG sustains the good mechanical properties of metallic glasses, showing a high hardness of ∼5.3GPa. This work provides new insights into glass formation, offers the opportunity for further studies of the physical and chemical properties of this new type of non-crystalline solid, and promotes the applications of metallic glasses as catalysts, which may trigger intensive research in materials science.