Abstract: In order to optimize the ultrasonic- assisted extraction of γ- glutamyltranspeptidase( GGT) from Toona sinensis,single factor investigations were initially carried out,followed by construction of a three- factor,three- level Box- Benhnken experimental design,quadratic regression fitting for GGT activity as a function of three extraction conditions and response surface analysis.The optimal conditions for the ultrasonic- assisted extraction of GGT were volume of buffer solution of 240 m L( 10.00 g),ultrasonic power of 260 W,and ultrasonic time of 28 min. Under the above conditions,the experimental value of GGT activity was 7.188 U / g,which was in basic agreement with the model predicted value.