A stainless steel for use in a fuel cell separator is produced by subjecting stainless steel containing 16 mass % or more of Cr to electrolytic treatment and thereafter to immersion treatment in a solution containing fluorine. The electrolytic treatment is carried out by anodic electrolyzation or by a combination of anodic electrolyzation and cathodic electrolyzation, and an anodic electrolytic quantity Qa and a cathodic electrolytic quantity Qc preferably satisfy Qa≧Qc. The solution containing fluorine preferably has a temperature of 40° C. or higher, and hydrofluoric acid concentration [HF] (mass %) and nitric acid concentration [HNO3] (mass %) satisfying [HF]≧0.8×[HNO3].