Analysis to be found in the article is based on data of mass polls carried out in the period of 1992 to 2003 by leading Russian and Ukrainian organizations studying public opinion; and the subject of the analysis is transformations that have been being undergone within, respectively, Ukrainian and Russian societies by habitual ideas of the key objects of the respective countries' socio-political and national-state development, as well as by, respectively, Ukrainian and Russian societies' vision - and attitude as regards eventual adoption - of Western institutions and values. The authors are considering, in the comparative-historical aspect, the problems of assimilation by mass consciousness in both these post-Soviet countries, of such Western political institutions and values, as multiparty system, the presidency institution, parliamentarism, the institution of free elections, the values of democracy, market economy, freedom, human rights, tolerance to one's neighbors; they disclose the main factors which determine the features of similarity and of distinction in the functioning of Western political institutions in the Ukraine and in Russia. Special attention is given to discussing the alternatives and the recently outlined distinctions in the socio-political development of the Ukraine and of Russia, with due regard to cultural traditions proper to each of them, to the respective socio-psychological archetypes, to the inertia of political experience; the just mentioned factors' influence is demonstrated, on the prospects of these countries' modernization and national-political consolidation.