This study examines the Eco-Schools Project, a specific work of green schools that includes standards about building, renovating, and maintaining schools as physical spaces. The study aims to find out what the principals of eco-schools are thinking about sustainability and schools’ physical conditions, and how the schools are being shaped with the project. It is considered that the study will contribute to the limited literature on principals’ perceptions about physical space conditions and how they can build a sustainable school in Turkey. The study was conducted with 14 eco-schools’ principals in Istanbul. The data were collected by the interviews about sustainability and physical space, and two observations about sustainability and the physical space. The method of the study is phenomenology, and the data evaluation techniques are content and document analysis. In conclusion, while sustainability is seen as a factor that maintains the ecosystem by protecting natural sources, school facilities are insufficient for maintaining sustainability due to a lack of physical and financial possibilities and participation. Additionally, inadequacies about the Eco-Schools Project make sustainability processes more difficult. It is suggested that education stakeholders’ should be encouraged responsibilities and collaboration to enhance their sustainability perceptions and physical space conditions.