The etching process of thin films of Co0.87Nb0.10Zr0.03 in HF-free solutions containing H2SO4 and H2O2 was investigated by kinetic and electrochemical experiments. Etching involved the simultaneous oxidation of the alloy and reduction of H2O2. During etching, a a Nb oxide is formed on the surface, which is dissolved by H2O2 and H+. A rate equation is derived that describes the influence of both H2SO4 and H2O2 on the etch rate.