By use of an opposed jet diffusion flame technique, the effect of addition of a variety of gases to the silane combustion which proceeds through the following two gross reactions, Sill + 02 --* SiO2(s) + 2H2 (1) and Sill + 202 --' SiO2(s) + 2H20 (2), has been studied. On the basis of their inhibition effect, the additive gases could be classified into three groups. The first group, which included N2, CO2, and CF4, showed almost no inhibition effect. On the other hand, the addition of the second group gases such as CF3Br and CF3H changed the color of the flame and lowered the flame temperature. At the same time, a large production of H2 was observed in the exhaust gas. Ignition and extinction properties, however, did not vary in the presence of these gases. It was concluded that the progress of the gross reaction (2) was considerably retarded by the second group gases. Ethylene, as a third group gas, strongly inhibited the ignition and also made it difficult to maintain the flame of a low silane content. Ethylene must interfere in the progress of the gross reaction (1) due to its high reactivity against atomic and radical species. These additive effects are discussed on the basis of a silane combustion mechanism where the important chain carrier is the Sill3 radical.