The article studies quantitative and spatial dynamics of the Russian speaking population of the post soviet Ukraine. The factors accelerating the demographic shrinkage of the Russians of the country by 3 million people from 11.36 to 8.33 million during 1989–2001 are analyzed. The internal structure of such reduction is determined as the ratio of natural decrease, migration and assimilation. On the basis of a comparative analysis of the results of the 2001 Ukrainian census and the data of the ethnic and linguistic surveys of the Ukrainian population the conclusion is drawn that the core role in a prompt reduction of the number of the Russians belong to the assimilation whose importance is especially considerable during the first post war decade. The analysis of the dynamic trends of the last several years allows affirming that within the borders of the modern Ukraine without the Crimea and the Donbas which is politically independent from Kyiv there may live about 4.1–4.5 million Russians. The study of eventual middle term prospects prove that by 2020 the given number may reduce to 3,0–3,5 million people. The important role in this process will play all three factors of the number dynamics: natural decline, outward migration flow, assimilation. But the core role in the demographic shrinkage of the Russian community belongs to the assimilation or the transition from the Russian to the Ukrainian self identity of a part of the biological and ethnic community of Ukraine. However the number of the Russians in the country recorded by all ensuing censuses of the population was lower than the real ethnic and cultural presence of the “Russian world” in Ukraine as the above mentioned identity transfer was not accompanied by an acculturation. The Russian language and culture not only dominate in the Russian environment but also keep a weighty role within the dominant country group. Only by prolongation for a couple of decades of a severe anti Russian course Ukraine is capable of undermining the social and cultural potential of the Russian world, is capable of completing a “formal” assimilation of many millions of biological and ethnic representatives of a nation by an internal acculturation that will considerably accelerate the process of the demographic shrinkage of the Russian community of the country and will definitely make it irreversible.