The corrosion behaviors of ferritic/martensitic steel P92, austenitic stainless steel TP347HFG and HR3C have been investigated in supercritical water (SCW) at 550°C under 25MPa with 2ppm dissolved oxygen. After 600h exposue, all the samples formed a stable oxide layer, but of varying thickness and microstructure. A typical dual-layered oxide film on P92 and a single-layered structure on TP347HFG and HR3C were observed by SEM and EDS. Further XRD studies indicated the compositions of oxide layers weren’t independent to the type of the used steel. In comparison with ferritic/martensitic steel, austenitic steel showed a higher corrosion resistance.