Abstract: Signal averaging technique was used to detect the weak photoelectric responses. at the interface of unpretreated 1Cr18Ni9Ti stainless steel electrode/solution over the visible range of radiation. Photoresponse of open-circuit electrode potential curve and potential dependence of the peak-peak photovoltages were obtained quantitatively for the first time. Similarity between the photoresponses of stainless steel and those of thicker Fe_2O_3 film suggests the existence of very thin n-type semiconductor film on the surface of stainless steel and the applicability of semiconductor physics to such thin film within proper limits. This technique may be developed into and improved in-situ method to characterize the structures and passive films at various metal/solution interfaces.