The Open Access and Open Science movement is transforming the global research landscape by promoting openness and transparency in scientific processes. For Ukraine, joining this movement is particularly significant in the context of integration into the European Research Area and post-war reconstruction. The article analyzes the role of the State Scientific and Technical Library of Ukraine as a key actor in building the national Open Science ecosystem, its contribution to shaping policies and culture of Open Science, challenges and development prospects. The study is based on analysis of international and national documents, statistical data and practical experience of SSTL Ukraine. Results show that despite progress (136 repositories, over 90% open access journals), significant challenges remain in implementing FAIR principles, research data management and fostering Open Science culture among researchers.