The studies of a conversion of KCl with H2SO4 into KHSO4 were performed using a reactor associated with direct contact membrane distillation (DCMD). Polypropylene (PP) capillary membranes were used in the experiments. The feed comprised of solutions containing I mol of KCl with various initial concentrations of H2SO4, equal to 1, 1.25 and 2 moles. The feed temperature at the inlet of the module amounted to 343 K and permeate 293 K. The reaction mixture was concentrated close to the saturated state, when crystals of KHSO4 were precipitated from the solution after cooling. The mother liquor after separation of the precipitate was again concentrated by membrane distillation (MD). At DCMD operation conditions the transfer of water vapour and hydrogen chloride from the reaction mixture through the pores of hydrophobic membranes took place, whereas the non-volatile components were totally retained and continuously concentrated in the feed. It was found that amounts of hydrochloric acid in the permeate as well as amounts of KHSO4 salt precipitated from the reaction mixture increased with a rise in the sulphuric acid concentration in the feed.