A highly efficient method for preparing a diphenylsiloxane-dimethylsiloxane copolymer having a narrow molecular weight distribution, said method comprising:(I) polymerizing(A) a mixture of hexamethylcyclotrisiloxane and hexaphenylcyclotrisiloxane, using as polymerization initiator(B) a lithium compound having the formula ##STR1## in which R independently denotes a monovalent hydrocarbon radical, X and X' are selected from the group consisting of hydrogen and lithium, with the proviso that one of X and X' must be lithium, and m is an integer having a value of at least 1, optionally, in the presence of(C) a molecular-weight regulator selected from the group consisting of water and a compound having the formula ##STR2## in which R has its previously defined meaning and p is an integer having a value of at least 1, said polymerization taking place in the presence of both(D) a nitrile compound and(E) an active hydrogen-free polar solvent; and(II) terminating the polymerization reaction product from step (I) with a neutralizing agent selected from the group consisting of an acid and an organohalosilane.