Electrochemical intercalation-deintercalation of 18 M H2SO4 into graphite is examined in the acid solution free and admixed with 0.5 M MoO3. The differences observed in the kinetics of reactions resulting from the presence of MoO3 in H2SO4 allow an assumption that negatively charged molybdenum oxide and/or its intermediates are intercalated into graphite galleries together with sulphuric acid producing ternary H2SO4-MoOx-graphite intercalation compound (GIC).