In modern Ukraine, trade plays an important role. Thus, the issue of studying the history of the development of a merchant class as a trade relations carrier in Southern Ukraine is relevant. In general, the merchant class was a unique estate, which put atop not the social status but the fortune, i.e. readiness for active trade. The studying of the merchant class increase in number issue makes it possible to find out from which social strata the new representatives of the merchant class were coming. The goal of the paper is to study the peculiarities of Mykolaiv city merchant class increase in number during the 19th century. The objectives of the paper are to study the peculiarities of involving persons in the merchant class, to explain the reasons for the transition of ordinary citizens to the merchants of Mykolaiv, to highlight the peculiarities of submitting documents to the city authorities for registration as the merchant, and to study some cases of passport issuing. Certain attention is paid to the peculiarities of the increase in number of city merchant class with representatives of other strata during the formation and evolution of a merchant stratum of the city during the 19th century. Particular consideration is given to the role of the ordinary citizens in the formation of the merchant class of Mykolaiv and the specifics of their entry into the stratum. The social status of the persons who went over to Mykolaiv merchants from other cities of the Russian Empire is defined.