Objective:To optimize extraction process of volatile oil from Croton crassifolius. Method:Volatile oil from C. crassifolius was extracted by steam distillation method

with "overall desirability" of yield of volatile oil and the concentration of cypenrenoic acid as dependent variable

the amount of water

soaking time and extracting time were investigated by central composite design

test data were fitted by multi-linear equation and second-order polynomial equation

extraction technology conditions were optimized by response surface methodology and to predictive analysis. Result:Multiple correlation coefficients from second-order polynomial equation(r=0.993) were prior to those from multi-linear equation(r=0.804)

optimum extraction process conditions were as follows:soaked 101.75 min with 17.57 times the amount of water

distillation time of 321.29 min;under these conditions

average yield of volatile oil was 4.06%

extracting amount of cypenrenoic acid was 0.143 mg·g-1

deviations between observed and predicted values were less than 3%. Conclusion:This optimized process was simple with high predictability

it could provide test basis for resource development of C. crassifolius.