A sulfide chain-bearing organosilicon compound having the average compositional formula: (R.sup.1O).sub.(3-p)(R.sup.2).sub.pSi--R.sup.3--S--(R.sup.4--S.sub.m).sub- .q--R.sup.4--S--R.sup.3--Si(OR.sup.1).sub.(3-p)(R.sup.2).sub.p is prepared at low costs and in high yields by reacting a halogen-terminated organosilicon compound having the formula: (R.sup.1O).sub.(3-p)(R.sup.2).sub.pSi--R.sup.3--S--R.sup.4--X, sulfur, and optionally a halide having the formula: X--R.sup.4--X with an aqueous solution or dispersion of a sulfide M.sub.2S or hydrate thereof in the presence of a phase transfer catalyst. R.sup.1 and R.sup.2 are monovalent C.sub.1-4 hydrocarbon groups, R.sup.3 and R.sup.4 are divalent C.sub.1-10 hydrocarbon groups, m has an average value of 2-6, p is 0, 1 or 2, q is 1, 2 or 3, X is halogen, and M is ammonium or alkali metal.