Effects of cold work and aging treatment on corrosion and microhardness of duplex stainless steels were studies employing weight-loss tests, polarization tests and micronardness test. Degree of cold work applied were 15%, 30% and 40%, and temperatures for aging were 475℃, 600℃ and 800℃. Cold work enhanced the corrosion resistance, and this fact was attributed to decrease in the amount of ferrite and change in its configuration. Cold work higher than 15% was detrimental, because increase in defect concentration counteracted against the beneficial effects of ferrite. Aging treatment improved the corrosion resistance and the hardness. Spinodal decomposition at 475℃ and ferrite-austenite transformation at higher temperatures were attributed to the improvements. Applying 30% cold work followed by aging heat treatment at 475℃ was found the best in treating the duplex stainless steels studied.