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The main reason for the study of Fe-based (FINEMET and NANOPERM) alloys was their magnetic properties. The nanocrystalline phases α-FeSi and α-Fe are responsible for the soft magnetic properties of FINEMET and NANOPERM alloys, respectively. A new type of amorphous and nanocrystalline FeCo-based alloy (HITPERM) has recently been produced. Its soft magnetic properties, which are attributed to the formation of α′-FeCo phase during the crystallization process, persist to the α–γ phase transformation at 980 °C. In spite of that the magnetic properties have got attention, the corrosion process on these amorphous and crystalline alloys became important due to the loss of magnetic properties. FINEMET alloys are more resistant to corrosion process than NANOPERM alloys in function of its Si content that acts on protector film formed during corrosion attack. The present work compares the magnetic flux density and the corrosion resistance in acid media of FINEMET, NANOPERM and HITPERM alloys, quantifies the losses on magnetic flux density due to corrosion process and introduces a new corrosion data about the amorphous and crystalline FeCoNbCuSiB alloy.