This research explores the application of the Sustainability Triangle in the development of forest city to address critical environmental challenges facing modern urban areas, with a special focus on the development of forest city in Indonesia's new capital city (IKN). Forest cities integrate extensive vegetation into the urban environment, offering an effective ecological solution while providing significant economic and social benefits. By improving air quality through the absorption of carbon dioxide and other pollutants, urban forests contribute to a healthier urban atmosphere. Additionally, urban vegetation helps reduce the urban heat island effect by lowering surface temperatures and reducing energy requirements for cooling. Urban forests also function as habitats for various flora and fauna, increasing biodiversity and ecological balance. Analysis carried out on existing urban forest projects at IKN, highlights the important role of commitment and collaboration between government, the private sector, local communities, and research institutions in the success of these initiatives. Policy recommendations, such as increasing community participation, adopting environmentally friendly technologies, diversifying plant species, and developing supportive policies, aim to strengthen and optimize the implementation of urban forests. This research makes a significant contribution to the academic literature and practice of sustainable urban development, demonstrating that the forest city concept is an effective and comprehensive approach to addressing urban environmental challenges. It is hoped that the sustainable development and implementation of this concept can create future cities that are more environmentally friendly, economically competitive, and socially prosperous.