Abstract: Solutions of tetraethylammonium and lithium chlorides in acetonitrile were studied by electronic absorption spectroscopy. It was shown that at concentrations up to 100 mmol/L tetraethylammonium chloride completely dissociates. The association constant of lithium chloride in acetonitrile (K_ass = 4800 mol^–1 L) was determined by the spectrophotometric method. The electronic absorption spectra of the Li⁺Cl^– ionic pair and Cl^– anion in acetonitrile were studied.