In the present work, the laminar premixed acetylene-hydrogen-air and ethanol-hydrogen-air flames were investigated numerically. Laminar flame speeds, the adiabatic flame temperatures were obtained utilizing CHEMKIN PREMIX and EQUI codes, respectively. Sensitivity analysis was performed and flame structure was analyzed. The results show that for acetylene-hydrogen-air flames, combustion is promoted by H and 0 radicals. The highest flame speed (247 cm/s) was obtained in mixture with 95% H-2-5% C2H2 at lambda = 1.0. The region between 0.95 < X-H2 < 1.0 was referred to as the acetylene-accelerating hydrogen combustion since the flame speed increases with increase the acetylene fraction in the mixture. Further increase in the acetylene fraction decreases the H radicals in the flame front. In ethanol-hydrogen-air mixtures, the mixture reactivity is determined by H, OH and O radicals. For X-H2 < 0.6, the flame speed in this regime increases linearly with increasing the hydrogen fraction. For X-H2 > 0.8, the hydrogen chemistry control the combustion and ethanol addition inhibits the reactivity and reduces linearly the laminar flame speed. For 0.6 < X-H2 < 0.8, the laminar flame speed increases exponentially with the increase of hydrogen fraction. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.