A process for preparing aminopropyl alkoxy silanes comprising reacting an allylamine having at least one active hydrogen atom attached to the amine nitrogen atom with a hydro-alkoxy silane having from 1 to 3 alkoxy groups attached to the silicon atom in the presence of a rhodium complex having inorganic ligands, at least one of said ligands being carbonyl. By this process the desired gamma-isomer can be prepared in a high selectivity and yield within a short reaction time. When the reaction is carried out in the presence of carbon monoxide and/or a cyclic olefinic compound, the selectivity and yield of the gamma-isomer can be further improved. The presence of carbon monooxide in the reaction system further serves to lengthen the catalyst life and to reduce the amount of the catalyst to be used.