Abstract: The microstructure, mechanical properties and marine corrosion resistance of hot-rolled ultra-low-carbon phosphorus-bearing bainitic steel sections were investigated so as to develop a steel specially used in sea water with its high toughness and resistance to marine corrosion. The results showed that adding 0.09wt% P in the steel can provide strong solution strengthening with weak effect on impact toughness within the temperature range from room temperature to -40°C. The fact is attributed to that P segregation at austenite grain boundaries is inhibited due to the competition between C, B and P atoms, thus weakening the cold brittleness caused by P atoms. Compared with the ultra-low-carbon bainitic steels with or without P, the corrosion rate of the ultra-low-carbon bainitic steel with high P content fully submerged in 3.5%NaCl solution decreases obviously. The complex effect of Cu and P elements promotes the formation of a dense inner rust layer to resist the further penetration of Cl^- in the solution.