The article discusses the main sources of information for studying the dynamics of the number and migration of Moldovan Ukrainians in the late XX – early XXI century (population censuses, state information resources, annual statistical compilations, center data Civil registry, military credentials, etc.). Their characteristic is given, the requirements that demographic information must meet in order to be used for analysis (completeness, detail and multi-aspect, reliability, consistency in the collection, generalization, publication and analysis of demographic data). We consider data from sources that can be used for research on this topic. The importance of using a system of accounting and collection of demographic data (accounting for the state of the population at a particular point in time and accounting for demographic events (births, deaths, marriages, divorces, as well as moving from place to place) for a given time period is noted.