—Protolytic properties of holmium tetraphenyl-porphyrinchloride were studied by the method of twophase spectrophotometric titration with potentiometric monitoring of pH of the medium. Apparent constants of the heterophase reaction of the exchange of an anion for the hydroxide ion were determined. It was found that the membranes based on holmium tetraphenylporphyrinchloride with dibutyl phthalate as a solvent-softener are selective to ions of alkaline earth metals (Ca2+ and Ba2+) in the region of pH > 7 over the concentration range from 1 up to 1×10–4 M. Selectivity coefficients were determined by two independent methods: the method of biion potentials and the method of mixed solutions. The found selectivity series coincides with traditional Hofmeister series for cations.