The aim of this work is to study the effects of austenitizing temperatures on the microstructure and electrochemical properties of a typical type of martensitic stainless steel (MSS) in 3.5 wt% NaCl aqueous solution. The microstructures of the experimental MSSs in different heat treatment states, such as annealed and quenched after different austenitizing temperatures, were characterized using SEM-EDS and XRD analysis. Electrochemical techniques, including potentiodynamic polarization and electrochemical impedance spectroscopy were also used to analyze the electrochemical behavior of the studied material in 3.5 wt% NaCl aqueous solution. The results show that the Cr-rich M23C6 carbides were precipitated during annealing, and then dissolved into the steel matrix during austenitization. An increase in the austenitizing temperature can reduce the amount of Cr-rich M23C6 carbides in the quenched steels, improving the homogeneity of Cr distribution. The pitting potential of the quenched samples increased with the austenitizing temperature, and the passive films that formed on the samples austenitized at higher temperatures were more protective against chloride corrosion.