This article addresses the relationships between international labour-related migrations and social capital in two ethnically heterogeneous local communities, outstanding by their inhabitants' high degree of spatial mobility. On the basis of the observations performed and in-depth interviews with migrants and experts, social networks built by the inhabitants were analysed, with particular attention paid to migration networks, and the meaning and role of social capital in the inhabitants of cultural borderlands' migrations, especially in the areas of migrants' lives such as job seeking, living together and dealing with difficulties, were discussed. It has been demonstrated that the international labour-related migrations influence the quality and type of social capital present in the ethnically heterogeneous local communities at cultural borderlands, although the direction and force of this impact are not equivocal and depend most of all on the strength and quality of primary ties in the migrants' community of origin, i.e. if the community was rich in the social capital resources, migrations may contribute to its growth, while for communities deficient in this resource, migrations may cause its continued diminishing.