The invention concerns the preparation of halogenated monoorganoxysilanes, of formula (I), ##STR00001## said compounds being useful as synthesis intermediate in organic chemistry. Said method for preparing monoorganoxysilanes consists in: using as starting product halogenoalkylsilanes of the (CH.sub.3).sub.2SiCl.sub.2 type and in substituting the silicon with a radical bearing a divalent unit bound to an electrophilic reactive group capable of reacting with at least an appropriate nucleophilic agent to form a functionalised monoorganoxysilane of formula (II) ##STR00002##