The term 'Belgrade apartment' is related to two periods and two phenomena: a)the concept of apartment in multiple-family buildings in Belgrade between the two world wars (1918-1941) and b)activities of 'Belgrade School' of architecture, formed during the 60's and 70's of the twentieth century. In order for a certain concept of apartment organization to be called 'Belgrade', it had to have clearly defined characteristics which set it apart from other typology of apartments built in its immediate surroundings, or it had to be created in Belgrade, and then spread further. Until today it has never been researched or explained what these characteristics of 'Belgrade apartment' were, as it has been defined in scientific literature as a creative and an authentic type of apartment organization in multiple-family buildings in collective housing. The research discussed types of characteristic concepts of room organizations in apartments built during the two periods, from 1918 to 1941 and 1960 to 1975. The aim of the research was to prove the hypothesis on the existence of the authentic concepts of Belgrade apartments which were designed in the mentioned periods.