The author examines the evolution of St. Petersburg and Moscow, the Russian capitals, into megacities under the influence of industrialization in the second half of the XIX century. The urbanization processes in these cities and the challenges they faced are analyzed within the body of the text. The source base is the materials of the statistics, journalism, travel guides and research papers on historical urbanism of the period. The article shows that in the second half of the XIX century, under the conditions of rapid industrialization, both capitals became the largest industrial and commercial centers of the Russian Empire, a situation which contributed to the rapid growth of the population of these cities and their urbanization. Both capitals faced urgent problems of large cities: housing, water and air pollution, which caused high morbidity and mortality among the population. At the same time, new urban trends emerged, in particular, zoning of urban space, and, both cities had al achieved considerable achievements in the modernization of their infrastructure: horse-drawn railways were constructed, gas, kerosene and even electric lighting was installed, and water was purified. Thus, in the second half of the XIX century, both Russian capitals went through the same purgatory that European capitals had gone through several decades earlier. While neither Moscow nor even St. Petersburg during this period had yet become attractive enough for tourists wishing to see the sights of a modern metropolis, nevertheless, both capitals grew to become appealing megacities in the early XX century.