Abstract: The influence of Mo in the rutile-type flux cored wires on microstructure and mechanical properties of the deposited metal was studied.Results show that nearly all the Mo in the wire was transferred to the weld metal. Slight amount of Mo could impressively improve tensile strength but deteriorate the impact toughness. With the content continuing to increase, Mo had a slight effect on strengthening the deposited metal, however, the impact energy continued to decline obviously. Microstructure analysis showed that austenite phase transformation temperature dropped and the precipitated carbides increased with the increasing of Mo content. As Mo content further increased, the carbides was reduced but M-A microstructure increasesd, resulting in a much worse toughness.