A process for preparing organo(poly)siloxanes of the formulaR.sup.1 R.sub.2 Si(OSiR.sub.2).sub.m (OSiR.sub.2).sub.n OHwhich comprises reacting a hexaorganocyclotrisiloxane of the formula(R.sub.2 SiO).sub.3with a sil(ox)anol of the formulaR.sup.1 R.sub.2 Si(OSiR.sub.2).sub.m OHin the presence of a catalyst which contains fluoride ions, in which R is the same or different and represents a monovalent, optionally substituted hydrocarbon radical, R.sup.1 represents a hydrogen atom or a monovalent, optionally substituted hydrocarbon radical, m is 0 or an integer of at least 1 and n is an integer of at least 3.An alkali metal fluoride or an alkali metal fluoride bonded to a support material is preferably used as the catalyst in the process of this invention.