Abstract: Co-precipitation protein was prepared from Tilapia muscle and defatted soybean meal by p H-shifting.Effect of p H value, mixing ratios of tilapia to defatted soybean meal, dissolving time on soluble protein yield was determined in the extraction process.And then effect of p H value on precipitated protein yield was examined as well.The results showed that the solubility of co-precipitation protein was best under the conditions of dissolution that the optimal p H value was 2.0, 3.0, 11.0, and 12.0, the tilapia to defatted soybean meal 1 ∶ 1, and the dissolving time of 30 min. The SDS-PAGE results showed that soluble co-precipitation protein bands of deep/shallow showed that the content of soluble co-precipitation protein of high/low ( protein degradation at p H2.0) .According to the distribution of molecular weight, it was found that the co-precipitation protein consisted mainly of myosin heavy chain, actin, myosin light chain, small molecule water soluble protein, three subunits of the antigen protein of 7 S and two subunits of the antigen protein of 11 S, which showed that the composition of soluble co-precipitation protein was complete.The precipitation condition of soluble co-precipitation protein was p H4.5.In the above four conditions, the recovered protein yields from tilapia muscle and soybean meal were 88.05% ~ 94.70% by acid/alkaline solubilization and precipitation processing.The co-precipitated protein powder, Co-p ( 1 ∶ 1) , was obtained by freeze-drying. The protein content was above 85%, the fat content was about 0.84%, and the ash content was less than 4.17%.The use of p H-shifting method was beneficial for the recovery of co-precipitated protein.