This study deals with the examination of the ethnic population data of the 1950 census. Previously, data sets for this census could not be analyzed because the data have only recently become available. In addition to the data of the six Slovak nationalities (Czechs, Slovaks, Russians, Poles, Hungarians, Germans), the ethnic data series contain data of other and unknown nationalities too. In this study, I examine the data on nationality broken down by administrative units (counties, districts), the size of municipalities, the proportion and number of nationalities living in the examined municipalities. I also examine the changes in the aggregate data of the majority and minority nationalities according to municipalities, as well as the changes in the individual nationalities separately. Based on the analyzed data, the patterns of the ethnic spatial structure of nationalities living in Slovakia at the time of the first census after World War II can be traced. Graphs and tables help to review the composition of the municipal structure of each nationality in a more nuanced way.