The analyses of interwar Vilnius heritage preservation, research, and maintenance concentrated mostly on discussions about the general law, state tendency, and case studies of good and bad practices. However, the more modern heritage preservation, research, or maintenance theories and aspects during the interwar period were neglected. Therefore, this article aims to analyse if modern technologies, ideas, and methods in the heritage research and maintenance (mostly in the reconstructions and adaptation of heritage buildings for new purposes) projects were adapted or not in interwar Vilnius. According to this aim, the article analyses a few heritage maintenance works and emphasises how architects used new technologies, modern architecture details, and ideas in the heritage maintenance projects and their realisation. Technologies as central heating system, electrification, canalisation, toilets, or bright interiors, wide air-spaces were inseparable from modernism perspective. The architecture of buildings and urban structures were modernised and improved for better living quality. Also, ideas and technologies did not avoid the heritage objects, especially civil buildings as Vilnius Town Hall, squares as Cathedral square, defensive heritage object as Vilnius Upper Castle. However, the analysis maintains that modern technologies were used moderately and kept a respectful tone with the authentic heritage, whole complex, and elements.