A diorganodichlorosilane is prepared by subjecting organochlorosilanes to disproportionation reaction in the co-presence of a SiH group-containing compound and in the presence of a primary catalyst of AlCl3 or AlBr3 and a co-catalyst of Mg, Al, Ca, Ti, Fe, Ni, Cu, Zn or Sn or a compound thereof. The invention enables disproportionation reaction of organochlorosilanes under atmospheric pressure and at a low temperature at which no substantial sublimation of AlCl3 or the like occurs, thus allowing the reaction equipment to be simple and improving the safety of reaction.