NiW alloy catalysts were prepared on a Cu foil substrate by using a co-electrodeposition method for use in the hydrogen evolution reaction (HER) in alkaline water electrolysis. The compositions of the alloy catalysts were controlled over a wide range by varying the molar ratio [W⁶⁺]/[Ni²⁺] in the electrolyte. At high W contents (∼41 at.%) in the deposited catalyst, the morphologies of the NiW alloys showed drastic changes compared with those of electrodeposited Ni, in particular a significant decrease in surface coverage and aggregates’ sizes. All of NiW alloys deposited in a citrate-containing bath demonstrated an amorphous structure, regardless of W content. Electrochemical measurements employing repeated cyclic voltammetry (CV) showed enhanced HER activities for the NiW alloy catalysts compared with the pure Ni catalyst. The maximum HER activity was obtained with a W content of 41 at.%; the alloying effects, including morphological changes, and the high affinity for hydrogen absorption shown by this alloy's amorphous structure are dominant factors in the enhanced HER activity. The results presented herein provide advanced information of significant relationship between material properties and HER activity of NiW alloys.