The article examines and summarizes the experience in using the components of the ecological security system in European cities, which ensure the solution of problems concerning sustainable development. The research used the methods of a systematic approach, analysis and synthesis, abstraction, logical generalization. The city's ecological security system is a set of economic methods and legal tools linked by the tasks of protecting the environment and creating comfortable living conditions for the population. Based on considering conditions and factors, the above methods and tools allow making decisions on supporting the ecologically safe development of the city. The experience of sustainably- developed European cities shows that their main ecological priorities at the present stage are the following: developing renewable energy; improving the energy efficiency of buildings and structures, reducing urban motor vehicle traffic in the central part of the city, using bicycles and urban electric transport; forming green spaces in order to strengthen ecosystem resilience and preserve biodiversity; rational handling of industrial and household waste. To achieve these priorities the following methods and tools are used: the development of a circular economy; introduction of resource-saving technologies and environmental innovations; formation of the ecological consciousness of the population; the broad powers of local governments in the environmental sphere, implementation of ecological programs and projects; support for environmental entrepreneurship. It was determined that to use the European experience of the ecological security system in Ukrainian cities, it is necessary to carry out preparatory work in the legal aspect (implementation of legislation and development of regulations, standard acts, provisions) as well as in the organizational and economic aspects (formation of conditions and opportunities for the implementation of decisions made in the environmental sphere). The preposition is made that the introduction of the individual components of the ecological security system used in European sustainably-developed cities should be done in Ukraine gradually, starting with eco-projects, eco-entrepreneurship, eco-cooperation and the formation of eco-spaces. The above components of the ecological security system must be aligned with goals and priorities of the sustainable development of the city in the economic and social aspects, which should be the subject of further research.