In order to increase protein content, rice residue, as a by-product in starch sugar process, was processed by ultrasound-assisted amylase treating. The effects of ultrasonic power, ultrasonic temperature, liquid-solid ratio, enzyme amount, enzymatic time on rice protein purity were investigated by single factor analysis. The technical parameters were further optimized by orthogonal experiment. The result showed the optimal condition was as follows: ultrasonic power 120 W, ultrasonic temperature 60 ℃, enzyme amount 50 U/g, liquid-solid ratio 12∶1 and enzymatic time 140 min. Under the above-mentioned optimum condition, the verification tests demonstrated that the purity and the recovery rate of protein were 82.4% and 87.5% respectively.