The invention is meant for chemical industry and is applicable in production of household sanitizers and detergents. A mixture of commercial tertiary amines or a mixture of straight-run tertiary amines is rectified and fed into the reactor for synthesis of a quaternary ammonium compound by a reaction of said mixture with benzyl chloride under stirring and at an elevated temperature. The mass ratio of the tertiary amines-benzyl chloride mixture is between 1.57 and 1.81. It is preferred that the use is made of benzyl chloride refined by distillation at the atmospheric pressure and a temperature of 177-178° C. The derived quaternary ammonium compound consists essentially of dimethyl dodecyl benzyl ammonium chloride and tetradecyl dimethylbenzyl ammonium chloride, the mass ratio of which is controllable. The product can be obtained in the form of gel. Where water or an organic solvent is added to the reaction mixture, a dissolved product is obtained. The product is free from alkyl radicals with the number of carbon atoms over 14, is low-toxic, and its purity is at least 95 mass %. The proposed invention renders it possible to use inexpensive and procurable raw materials, to lower energy intensity and process time, 1 claim, 1 fig., 3 tabl., 5 emb.