Behavior of a bisviologen and a carboxylated viologen in their faradaic phase transition at a highly ordered pyrolytic graphite (HOPG) electrode between a gas-like adsorption layer and a two-dimensional condensed phase was studied. Bisviologen (bis-V) possesses two 4,4′ -bipyridinium moieties, and a carboxylated viologen (V-COOH) does carboxyl groups at both terminals of the alkyl chains. The results of the voltammetric measurements were compared with heptyl viologen (HV) with a focus on the intermolecular lateral interaction among radical cations of the viologens in the condensed phase. It was found that the intermolecular attractive interaction between neighboring reduced forms of bis-V is stronger than that of HV, indicating that intermolecular stacking of two radical cation moieties per molecule appears dominant over the negative effect of the possible chance of the presence of out-of-gear molecule pairs due to the mismatch in the neighboring molecule stacking upon the transition. The potential width of the bistable region of the phase transition for V-COOH exceeded 120mV in an acidic medium due to the effective positive contribution of hydrogen bonding to the intermolecular attraction in the condensed phase on the hydrophobic basal plane of the HOPG electrode, while the contribution vanished in a basic medium. These results revealed that the voltammetric spike response of the phase transition can be a direct measure of the strength of two-dimensional intermolecular interaction on the electrode surface. Characteristics of the phase transition behavior of V-COOH were also described in regard to temperature, concentration, and potential sweep rate dependencies. Implications of these characteristics were discussed in consideration of the dynamics of the assembling process of reduced forms of V-COOH into the condensed layer. In the tests of the additives, only trimesic acid among the carboxylic acids used exhibited the activity as a hydrogen bonding inhibitor.