Tungsten carbide is an interesting non-noble metal anode electrocatalyst that can be passivated against corrosion in acidic electrolytes for use in low-temperature fuel cells. The structure of nanocrystalline WC passivated in 1.5 M H2SO4 at 65 °C was studied using synchrotron extended X-ray absorption fine structure spectroscopy and compared with the as-prepared material. Changes in the average local structure are noted that correspond to the development of an oxide phase in the material. This is most likely to be present as a WIV-oxide phase on the surfaces of the particles.