Abstract: Abstract: In order to reduce the degreasing rate and improve the quality of yak bone powder, the ultrasonic assisted organic solvent degreasing method was studied based on the thighbone of Qinghai yak in this paper, and the nutrient contents and physicochemical properties were analyzed comparing with the traditional boiling degreasing method. Firstly, the degreasing solvent was screened according to degreasing rate and applicability among four common organic solvents. Basing on the single factor test, Box-Behnken test was designed to optimize the parameters including ultrasonic power, degreasing time and the ratio of liquid to material. After that, the analysis of the degreasing rate, the loss rate of protein, collagen, main minerals and the microstructure of yak bone treated by ultrasonic and boiling was carried out. Subsequently, the particle size distribution, microstructure, chemical structure and calcium release rate of yak bone powder dealt with the planetary ball mill were shown as well. Results suggested that ethyl acetate was the optimal degreasing solvent with a higher degreasing rate and better applicability under the same conditions. In addition, the two regression model built by response surface design had a good fitting degree with the correlation coefficient of 0.9484 indicating that the model fitted well in the whole regression region. Considering the energy consumption, the optimum degreasing conditions were finally determined as follows: ultrasonic power is 500 W, ultrasonic time is 30min, and the ratio of liquid to material (mL/g) is 6, under which conditions the degreasing rate could reach 92.00%±0.20% and the relative error of the predicted value was 1.08% which was less than 5% revealing that the model was effective. Besides that, it was also found that the degreasing rate of ultrasonic (92.00%±0.20%) was significantly higher than that of boiling method (71.25%±2.31%) (P<0.05). Meanwhile, the loss rate of protein and collagen were 8.11%±0.48%, 11.05%±2.45%, respectively, which were dramatically lower (P<0.05). And there was a serious loss of Na, K, Fe, Mn in cooked yak bone that were 19.00%±1.44%, 58.95%±1.04%, 14.32%±2.46% and 20.86%±1.29% respectively while the loss about Fe, Zn, Mn in ultrasonic skimmed yak bone was slightly, and the contents of P, Ca, Mg, Cu, Se, Mo, Sr in the bone treated with the two methods were similar (P>0.05). As for the microstructure of yak bone, the boiling one was looser and more porous. After pulverization, the median diameter of ultrasonic defatted bone powder was (35.84±0.60) μm while the other was (11.73± 0.29) μm, which was in agreement with the result of scanning electron microscope. Moreover, no significant difference had been observed in the chemical structure, and there were mainly phosphate and carbonate in two kinds of bone powder. For the calcium release rate of bone powder, result indicated that both methods had no significant difference (P>0.05). In conclusion, the ultrasonic assisted organic solvent degreasing method could remain more nutrients with the higher degreasing rate. This study provided a high efficient degreasing method, which has the value for improving the processing technology for preparing the yak bone powder.