Alumina was extracted from oil shale ash which is a solid by-product of oil shale processing. A Box-Behnken statistical design was used to optimize the factors affecting the extraction efficiency of the alumina such as sulfuric acid concentration, reaction time and reaction temperature, and to determine the optimum conditions for the extraction process. The optimal extraction efficiency of 89.71% can be obtained when the conditions are as follows: the temperature of 100 degrees C, the time of 4 h and the sulfuric acid concentration of 50 wt.%. The result of statistical design shows that the extraction efficiency was in an agreement with the generated model and the experimental results. Further, the ultrafine silica powders were characterized by various techniques. The results show that the purity of alumina reaches 99.80%, which is suitable for the production of aluminum metal. It is evident that the way of extraction of alumina from the oil shale ash is practical and feasible and provides a new solution of the pollution to the environment. (C) 2010 Elsevier B.V. All rights reserved.