Abstract: Complex addition of Cu and Ni to the steel produces no ferrite phase, while steel corrosion resistance can be increased. The mechanism for complex addition of Cu and Ni contributing to enhance of steel corrosion resistance is that the corrosive membrana is non-crystal and that an enrichment layer of Cu is formed under the corrosive membrana. Therefore,addition of Mo,particularly higher than 1.5 % will enhance acidic atmosphere-resistance of the steel. Based on this research result, low C-13 %Cr-Cu-Ni-Mo steel tube has been developed. The steel tube is in possession of such properties as CO₂ corrosion resistance, acidic atmosphere-resistance and high strength and toughness,being capable of acting as a substitute of the dual-phase stainless steel tube in many cases.