By premixing a sulfide chain-bearing organosilicon compound, a halogenoalkyl group-bearing organosilicon compound, and optionally, sulfur, adding anhydrous sodium sulfide Na₂S to the premix, and allowing reaction to take place, a sulfide chain-bearing organosilicon compound having a shorter sulfide chain can be prepared in high yields and at a lost cost while minimizing formation of monosulfide-bearing organosilicon compound.