This paper attempts to review our recent work to provide an aspect of catalysis "surface catalytic reactions assisted by gas phase molecules", describing the previous representative results and also presenting new data. In this concept, reaction intermediates are activated by gas phase molecules which adsorb weakly or are undetectable at the surface. The examples are the ethanol dehydrogenation on Nb/SiO2, the water gas shift reactions on MgO, ZnO and Rh/CeO2, and the NO-CO reaction on Co/Al2O3.