Transition-metal dichalcogenides (TMDs) are promising electrocatalysts toward the hydrogen evolution reaction (HER) in acid media, but they show significantly inferior activity in alkaline media due to the extremely sluggish water dissociation kinetics. Herein, CoSe2/MoSe2heterostructures with CoSe2quantum dots anchored on MoSe2nanosheets are synthesized towards enhanced alkaline HER catalytic activity. The incorporation of CoSe2is intended to construct additional water adsorption sites on the basal planes of MoSe2to promote water dissociation. The CoSe2/MoSe2heterostructures show substantially enhanced activity over MoSe2and CoSe2in 1 m KOH. The optimal overpotential required to reach a current density of 10 mA cm−2is merely 218 mV, which is more than 100 mV greater than that of MoSe2, which is by far the best performance demonstrated for precious-metal-free catalysts. Detailed analyses based on electrochemical testing demonstrate that the water adsorption and subsequent dissociation process is accelerated by CoSe2species with rich edge sites; meanwhile, MoSe2species provide sufficient active sites for the adsorption and combination of adsorbed hydrogen (H.). These results provide an effective strategy for developing earth-abundant catalysts with high activity for the alkaline HER, and are of great significance to promote the practical application of alkaline water electrolysis.