The research aims to evaluate the microstructure, mechanical properties and marine corrosion resistance of P-bearing ULCB steels. P produced stronger solution strengthening effect, but had less effect on the low temperature impact toughness of ULCB steel. With increasing P content to 0.09(mass)%, the immersion corrosion rate of ULCB steel in 3.5% NaCl obviously decreased in comparison with those steels without or with lower P content. This is attributed to that the complex effect of Cu and P promoted the formation of dense amorphous oxyhydroxide in the inner scale, which inhibited further corrosion from NaCl solution. Mo in ULCB steel played an important role in avoiding pitting corrosion in Cl- environment.