The potentiokinetic curves of anodic polarization of magnetically hard Fe-28% Cr-24% Co-1% Si alloy in sulphuric acid of pH 0 were plotted. The Fe-Cr-Co-Si alloy has been subjected to four different treatments that are usually used for generation of magnetic properties. Research has shown that the heat treatment at temperatures of the order of 640 °C applied for generation of two-phase structure causes the drastic decrease of corrosion resistance of the tested alloy.