One of the main problems of monument protection and restoration is to determine the value of the object of protection, including its stylistic purity. The method of system-structural analysis helps to investigate and substantiate the manifestations of the main features of style at different levels - urban level, object level and level of a single element, and thus argue whether a building is an example of a particular style. The application of the method of system-structural analysis is shown on the example of objects of Ukraine in the Art Nouveau style. It was determined in the thesis the group of factors and conditions, which predominated the beginning and spreading of a cultural phenomena of Art-Nouveau style architecture in Ukraine. The investigation of street-line architecture in the Ukrainian cities with historical Art-Nouveau style buildings concentration allowed to ground the influence of Art-Nouveau style on the formation of squares and habitats architectural ensembles, individual buildings and their facades details. At the base of methodology of the systematic-structural analyze there were investigated for the first time the semantic properties of the architectural forms of Art-Nouveau style buildings in Ukraine. Also there were investigated the regional peculiarities of the typical composition methods of dwelling, public and industrial buildings creation in concentrating the attention on their facades that in this case mostly express the main characteristic of Art-Nouveau style. In the base of comparatively study of the Ukrainian Art-Nouveau style architecture with West-European and Russian examples there were determined the borders of two main architectural Art-Nouveau streams in Ukraine. Within these two main streams it can be found several basic and local centers of Art-Nouveau style in Ukraine that poses their individual features and specific of formation.