The effect of WC on cold spray deposition and erosive wear performance of Ni-WC composite coatings was studied. WC and Ni powders were fed to the gun from separate hoppers and a blend of Ni-36 vol% WC was sprayed onto mild steel substrates. By using three different WC powder sizes, the effect of WC size on coating build-up and WC retention were tested. Using smaller size WC particle, higher retention of WC into coating was achieved. Using macro-indentation, a relationship between mechanical properties and content of WC was studied. Detailed microstructural analyses and wear loss measurements were conducted to study mechanism involved in solid particle erosion (SPE) of Ni and Ni-WC coatings. One of the Ni-WC coatings with highest WC retention (10.5 vol% WC) was selected for SPE studies. Both Ni and Ni-WC coatings exhibited ductile erosion. Higher erosion resistance of coatings under normal angle compared to oblique angle was related to the formation of a protective tribolayer. It was found that 10.5 vol% WC content was too low to reinforce Ni against erosion under oblique angle. However, under normal angle, the addition of 10.5 vol% WC deteriorated Ni erosion resistance, by preventing tribolayer formation and brittle fracture.