Ultrasonic Assisted Drilling (USD) is new technique to drill difficult to machine materials. In this method, tool or workpiece vibrates with amplitude of few microns in addition to conventional drill bite rotation. In this experimental research, the bone was drilled both conventionally and using UAD, then the thrust was measured in two methods at feed rates of 50, 75 and 125 mm/s and 500, 710 and 1000 RPMs. The results show that USD method causes the thrust force decreases considerably in compare whit conventional drilling. The maximum temperature is less in USD at low RPMs.