Abstract. In the first post-war years, New Belgrade denoted a concept of a new city on the left bank of the Sava River, opposite to historical Belgrade. Initially, it was planned as a capital of Yugoslavia, a centre of administration, culture and economy. However, its basic purpose changed in the following years. As elsewhere in post-war Europe, affordable housing was high on the agenda. Therefore, New Belgrade was eventually realized as a city of housing mega-blocks, as an answer to the housing needs. In the period that followed, urban development strategies and policies were changing, thus New Belgrade passed through different levels of transformation. Today, the modern blocks are left to decay, while the urban pattern of New Belgrade is being altered once again, now by market-oriented urban practices. This paper investigates the metamorphosis of New Belgrade, and analyses the housing blocks in order to present their values and to contribute to the preservation issue, but also to highlight their current condition and need to be adapted. Furthermore, it aims to rethink the adaptive capacity of applied prefabricated systems: it investigates if their flexibility and modularity can provide adaptability of the structures to today’s requirements. The analysis is conducted through a comparison of two buildings in Block 23: two prefabricated systems - panelised and IMS (Institute for testing of materials) skeleton system, layouts and appearance. Their ability to adapt to the contemporary context and needs is recognized as one of the most important criteria in the analysis on how sustainable the mega-blocks are.