Biomass gasification has received much attention in recent years due to efforts in finding alternatives to fossil fuels. However the inefficiencies of the process and also the by-product produced during the gasification makes this process unsuitable for commercial applications. Thus, catalyst is used to improve the product gas quality and to reduce the tar formation. Commercial catalyst such as dolomite, nickel and olivine are widely used in biomass steam gasification, but it has limitation such as short active lifetime and expensive. The potential of the bottom ash as the substitute catalyst in biomass steam gasification is discussed, thus the characterization of the bottom ash is performed to determine the surface morphology, chemical compound, pore size, pore volume, surface area and bulk density of the bottom ash. The result shows that the bottom ash contains elements such as SiO2, Fe2O3, Al2O3, CaO and MgO which have been used as the catalyst in biomass steam gasification. The pore volume of the bottom ash is 3.01 nm which falls into mesoporous category and the pore volume is 0.04 cm3/g with surface area of 58.01 m2/g and bulk density of 2.53 g/cm. © 2016 The Authors. Published by Elsevier Ltd.