This work describes an experimental study of the effect of hydrogen addition on the stability and impingement heat transfer behaviors of a biogas diffusion flame. The amount of hydrogen added was varied from 5% to 10% of the biogas by volume. The results show that upon hydrogen addition in the biogas flame, there is a corresponding change in the appearance, stability and heat transfer characteristics of the flame. Addition of hydrogen significantly enhances the stability of the biogas flame, and the initial 5% hydrogen addition is found to be more efficient in the stability enhancement than the other 5% hydrogen addition. As the component CO2 in the biogas is replaced by N-2, the stability limit can be further enhanced, indicative of a more adverse effect of CO2 than N-2 on flame stabilization. Compared to the CH4-N-2 flame, the biogas flame (CH4-CO2) has lower flame temperature and lesser soot emission. For both flames, the effect of hydrogen addition is to increase the flame temperature and reduce the flame height. The heat transfer data show that the stagnation point heat flux is enhanced by hydrogen addition due to the fact that there is higher flame temperature at higher level of hydrogen addition. While the total heat transfer rate is lowered because hydrogen has lower energy content per unit volume than the biogas substituted. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.