One of the last tasks during constitution of federal and republic organs in the second Yugoslavia was that of territorial and administrative organisation of the new state. According to directions of federal authorities, departments for the development (»building«) of people’s power were organised at republic organs, to fulfil purpose of inter-republic demarcation and definition of territorial organisation inside federal units. In Croatia Department for the Development of People’s Power was organised at those days Presidency of the Croatian People’s Government. Commission for the Boundary Demarcation was also established at the Presidency, with two sections, one preoccupied with external boundary demarcation (i.e. with the cases in which republic boundaries were the same as federal), and another one which was preoccupied with inter-republic demarcation issues. Commission was active in the period between June 1, 1945 and December 31, 1946, respectively till February 17, 1947. Results of the international section’s activities are presented in a big number of publications which were significant support to Yugoslav diplomatic efforts in front of international authorities engaged in after war boundary demarcation. Contrary to that, arguments relevant for the inter-republic demarcation were not published, what speaks clearly of methodology used by Communist Party in the solution of interethnic relations. Both parts of the Commission were connected in their work with numerous bodies and institutions. Especially strong relations existed between »international« section of the Commission and Institute for the International Relations of the Ministry of Foreign Affairs in Belgrade, and with Adriatic Institute in Rijeka. The last one was serving as neutral »label« under which Commission emerged as a publisher, but also as a label under which Commission’s members were presenting official politics abroad. Except recognised, and even today useful value in the context of external boundary demarcation of Croatia, and its significance for the general demarcation history in 1945, archival documents from the Commission’s fonds have additional archival value containing, in official gazettes not published, but for the administrative history important data: on Commission’s establishment, organisation, work modes and connections with other political and science bodies and organisations.