The present invention relates to a method for producing monosilane and tetraalkoxysilane comprising subjecting alkoxysilane represented by formula (1) HnSi(OR)4−n  (1) wherein R represents alkyl group having 1 to 6 carbon atoms and n represents an integer of from 1 to 3, to disproportionation reaction in a gaseous phase in the presence of an inorganic phosphate or a catalyst having a specific chemical structure based on a heteropolyacid salt structure. In the production method of the present invention, separation from the solvent can be carried out easily, the reaction proceeds quickly and the conversion rate of the starting materials is high.