Corrosion behavior in simulated pressurized water reactor (PWR) primary water was investigated for stainless steels with 16 and 22 wt% Cr having austenitic, ferritic, and duplex microstructure. For alloys with 22 wt% Cr, the Cr-rich inner oxide layer consisted of Cr2O3 and FeCr2O4 is formed. For alloys with 16 wt% Cr, the Cr-rich spinel inner oxide layer is formed. In-situ and ex-situ electrochemical impedance analyses and Mott-Schottky analysis was used to rank the corrosion resistance of the alloys. In addition to chemical composition, the phases (ferrite, austenite, and B2-NiAl) also affect the corrosion behaviors of the alloys.