The cavitation erosion behavior of Fe-Cr-C-Si-xMo (x = 0, 3 and 6 wt.%) hardfacing alloys were investigated for up to 50 hours by using 20 kHz vibratory cavitation erosion test equipment. With increasing Mo contents, M 23 C 6 and M 6 C carbides were formed instead of Cr-rich M 7 C 3 and M 23 C 6 type carbides observed in the interdendritic region of the Mo-free Fe-Cr-C-Si hardfacing alloy. This microstructural change was responsible for the improvement of mechanical properties such as hardness and cavitation erosion resistance of the Mo-added Fe-Cr-C-Si hardfacing alloy.