Abstract: Exposure buildup factor for some flyasheslike Bituminous, Subbituminous, lignite, high calcium, high iron, low calcium, low iron has been calculated in the energy region 0.015-15.0 MeV up to a penetration depth of 40 mfp. The five G.P. fitting parameters have been used to calculate EBF. Variation of EBF with incident photon energy and penetration depth has been studied. It has been observed that chosen flyash have maximum value of EBF at 0.3 MeV. Variation in value of EBF is due to dominance of different interaction processes in different energy regions. Comparison of calculated exposure buildup factor with standard shows good agreements.