This work has explored the surface modification of SiC submicron- and nanoparticles, and its influence on the particles' chemical behaviour and deposition rate in the electroplating of composite Ni/SiC coatings. SiC particles with different sizes (50, 60, 300 and 500 nm) were codeposited in their “as-produced” state. The ζ-potential measurements and alkaline titration for the “as-produced” particles showed differences in chemical behaviour for particles of different sizes, reporting pH buffering effect, even though the particles were inert and chemically the same (SiC). A surface treatment (ST) based on nitric acid was developed in an attempt to set a similar surface state, therefore a similar chemical behaviour in all particles. The ζ-potential measurements and alkaline titration of the “surface treated” particles showed similar results, independently of the size of particles. The pH buffering effect also decreased considerably by the ST. The codeposition rate was modified by the ST differently for each size compared to their as-produced state. The content of SiC50 and SiC500 was doubled (≈2% and ≈19%), tripled for SiC300 (≈7%) and more than halved for SiC60 (≈2%). The microhardness of these composite deposits was linked to the changes in the SiC codeposition.