The influence of cold working and grain size on the pitting corrosion resistance of Fe-Cr-Nb-Mo ferritic stainless steel is investigated using optical microscope and electrochemical methods. The pitting corrosion resistance firstly decreases with increasing the cold-rolling reduction from 0% to 30% due to the number of nucleation site increasing. With increasing the cold-rolling reduction from 40% to 60%, the disappearance of grain boundaries, stacked dislocation and uniform microstructure results in the pitting corrosion resistance of the steel. With prolonging the annealing time, the grain size of the steel grows, and the pitting potential of the steel decrease. The smaller grain size promotes the formation of compact passive film and improves the pitting corrosion resistance.