Abstract: Nutritional powder was made by extrusion using twin- screw extrusion technology with wheat germ and brown rice.The effects of water content in raw materials, screw speed, barrel temperature and the ratio of materials on quality indices including expansion degree and gelatinization degree of extruded powder were investigated.Response surface central composite design was used to determine the optimal process parameters for the preparation of nutritional powder as follows: wheat germ content was 37%, water content in raw materials of 19%, screw speed of 122r /min, and barrel temperature of 120℃.Verification experiment showed that the radial expansion degree and gelatinization degree were 1.54 and 93.3%.The results were similar to forecast and believable.Essential amino acid content of nutritional powder was much closer to the FAO /WHO model of the human body essential amino acids than raw material.