The invention relates to a method of preparing polyorganosiloxanes containing at least one functional group using a lithium silanolate catalyst. A polyorganosiloxane, having at least one hydroxyl group, is reacted with a polyalkoxysilane having the formula (R1)a(R2)bSi(OR3)4-(a+b) (I), where R1 is an alkyl radical, a cycloalkyl radical, or an aryl radical; R2 is —(Z)m-(X)n, wherein m=0 or 1, n=1 or 2; Z is a divalent hydrocarbon residue; X is an unsaturated hydrocarbon radical when m=0 and, when m=1, X is chlorine, bromine, iodine, —O—CO—CR4═CR5R6 (in which R4, R5 and R6 each represent a hydrogen atom, an alkyl radical and/or a phenyl radical), —RF (in which RF is a perfluorinated residue), —NHR7 (in which R7 is a hydrogen atom, an alkyl radical, or a radical-R8—NH2, wherein R8 is Z), or —SH; R3 is an alkyl radical; a=0, 1, 2 or 3; b=0 or 1 and a+b=0, 1, 2 or 3, with the additional condition that the sum a+b=3, symbol b cannot be equal to 0. The method is performed in the presence of an effective quantity of a lithium organosilanolate catalyst having formula (R1)a(R2)b(OR3)3-(a+b)SiO−Li+ (II), wherein R1, R2, R3, a and b have the meanings indicated above. The method is performed without the addition of an aliphatic alcohol having the formula R3OH to the reaction medium.