The purification of crude octacosanol extract from transesterified rice bran wax was carried out by molecular distillation (MD). A central composite rotate design (CCRD) was used in order to optimize the experimental parameters: distilling temperature and vacuum degree. Through the response surface methodology (RSM), the optimal MD conditions were determined and the quadratic response surfaces were drawn from the mathematical models. The results suggest that the distillng temperature and vacuum degree significantly affected both octacosanol content and yield of purified products, while the interaction of distilling temperature and vacuum degree was not significant in the two models. The optimum conditions of the purification of crude octacosanol extract were: distilling temperature 176.1 degrees C and vacuum degree 1.29 Torr. Optimal values predicted by RSM for the octacosanol content and yield of purified product were 25.93% and 51.09%, respectively. Close agreement between experimental and predicted values was obtained. (c) 2004 Elsevier Ltd. All rights reserved.