Abstract: Provided is a process for the preparation of polyorganosiloxanes containing unsaturated functions. A polyorganohydrogenosiloxane (A) containing at least 0.1 mol % of hydrogen atoms linked directly to the silicon is reacted with at least a stoichiometric amount of a hydrocarbon compound (B) having at least one ethylenic or acetylenic unsaturation, in the presence of a catalytically effective amount of a dehydrogenative condensation catalyst comprising a metal complex of formula (I): L.sub.n MR.sub.x Y.sub.y. M represents a metal chosen from titanium, zirconium and hafnium; the symbols L are the same or different and represent a hydrocarbon ligand of the metal M, the said ligand donating from 3 to 8 .pi.-electrons to the valence shell of the said metal; n is an integer ranging from 0 to 3; the symbols R are the same or different and represent a hydrocarbon or organosilicon ligand of the metal M, the ligand being a .sigma.