The paper investigates the mechanisms behind the formation and maintenance of those migrants’ social ties which translate into a particular composition of the network and become a source of social capital. Based on a number of in-depth interviews with Ukrainian migrants in Warsaw, we find that Ukrainian migrants’ networks are based primarily on ties homogenous in regard to nationality, level of education and character of work. The institutional context of social interaction determines with whom migrants form relations and whether these ties become a source of social advancement. The studied migrants do form bridging ties with more experienced, as well as socially and legally embedded persons, mainly other migrants, receiving both instrumental and emotional support.