This paper illustrates a comparative study of the effect of using hydrogen as a dual fuel in the intake mixture on exhaust emission characteristics of diesel and gasoline engines. There has been phenomenal technological advancements from the development of large external combustion engines to compact yet powerful internal combustion engines. With the advancement in technology and the stricter emission norms, there has been continuous effort to reduce the automobile exhaust emissions which are the major concern of the environment. Fuel economy improvisation and reduction of greenhouse gases from vehicular sources are the important research topics now. Of the numerous ways available, alternative fuels can be used to fully or partially replace the conventional petroleum based fuels. By making such a change we can benefit from the alternative fuels using existing internal combustion engine technology. In this paper, there is a comparative study of the effect of using hydrogen as a dual fuel in the intake mixture on exhaust emission characteristics of diesel and gasoline engines.