Heterogeneous catalysis of transesterification using KI/mesoporous silica catalyst was utilized to produce biodiesel from soybean oil and methanol. The effects of reaction temperature, percentage of KI loading, reaction time, and amount of catalyst on the conversion to methyl ester were studied. The results showed that increasing reaction temperature, KI loading and reaction time can enhance the conversion. The optimum condition was the reaction temperature at 70 degrees C, 15 wt.% of KI, a reaction time of 8 h., and a catalyst amount of 5.0% by weight of the oil which yielded 90.09% of the conversion. The fuel properties of biodiesel from the optimum condition were tested and found that only viscosity showed over standard. However, the high viscosity can be reduced by separation of non-reacting soybean oil. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.