The works of outstanding Russian scientists in exile M. I. Rostovtsev and G. V. Vernadsky on antiquity and ancient Russian history were included in the golden fund of historical science. The ethnogenesis of the Scythian--Sarmatian tribes has always interested researchers. Scientists have expressed a variety of assumptions and hypotheses of their origin. The Iranian nomads were linked with the Slavs, Germans, Mongols, Semites, Finns, etc. The conceptual approaches and conclusions of the two great Russian scientists abroad, M. Rostovtsev and G. Vernadsky, on the cardinal issues of the genesis and history of the Scythian--Sarmatian tribes are generally identical and correspond to the criteria existing in academic science. The article provides a comparative analysis of their views on topical issues of the ethnogenesis of the Iranian peoples in the light of new research within the framework of the given topic.