The catalytic activity of molybdenum disulfide (MoS₂) is associated with active sites located along the edges, whereas the MoS₂ basal plane is regarded to be inert. However, it is a great challenge to develop a rational way for producing active edges efficiently. Herein, we report a novel, cost-effective top-down process in which we can create a high density of active edge sites on MoS₂ basal plane by selective steam etching. The results show that the etched structure is strongly sensitive to the temperature, which creates 1D nano-channels, 2D in-plane triangular pits and 3D vertical hexagonal cavities on the MoS₂ basal planes by elevating the temperature. The edge configuration is revealed to exhibit a distinct crystallographic orientation. Furthermore, we evaluate the corresponding enhanced electrocatalytic activity for the hydrogen evolution reaction (HER) by measurements of the single etched MoS₂ samples in an electrochemical microcell, where the Tafel slope decrease by 49%, confirming the increased the density of active sites. In addition, the method is not limited to 2D materials in a flat geometry alone, but is also demonstrated on 0D MoS₂ particles by in-situ transmission electron microscopy. The steam etching reported here offers an alternative avenue to engineer the surface structures of MoS₂ facilitating the electrocatalytic applications of MoS₂ for hydrogen production.