In the present work the effect of silicon on the corrosion behaviour of Fe25Cr type ferritic stainless steels was investigated. It is shown that while an addition of 1 and 3% of silicon insignificantly change the electrochemical parameters, the addition of 5% reduces the critical passivating current density and the rate of cathodic reaction in H2SO4. At the same time a shift of passivation and stationary potential in the cathodic direction was observed. The conclusion was made that an addition of 5% of silicon increases the dissolution rate of Fe25Cr alloy in the active region. Some parameters of the electronic structure of alloys were used for qualitative explanation of the observed effects. A shift of s- and d-electronic density between the alloy components was detected by means of Mossbauer spectroscopy. It was demonstrated that silicon absorbs a sufficient amount of electronic charge density from iron and chromium. This effect leads to increasing the strength of iron-and chromium-water adsorption complexes and facilitates their release into the solution.