Canine femurs were ablated with an Er:YAG laser (2.94μm) with a pulseduration of 250μs. The bone ablation characteristics at four difierent pulse repetition rates (l-4Hz), were studied. The ablation depth versus energy density per pulse seems to follow an exponential function for large range of energy density. The increase of ablation ratio versus energy density at 1Hz was the highest, 2Hz the second, when the energy density levels were less than about 100 J/cm.