The purpose of this study is to develop and implement a young children's eco-logical transition education program based on the project approach, with the aim of exam-ining changes in young children's awareness of sustainable development, ecological liter-acy, and problem-solving abilities. The program was applied to 28 five-year-old children in E preschool located in S City focusing on the selected themes of ‘Marine Life’ and ‘Companion Animals and Animal Welfare’ during morning activities over an 8-week period. The collected data, including research journals, play observation logs, interviews, photo-graphs, etc., were qualitatively analyzed during the process of implementing the program To examine changes based on the timing of program implementation, quantitative data collected through observation checklists were subjected to repeated measures analysis of variance. The results of qualitative and quantitative analyses revealed positive changes in young children's awareness of sustainable development, ecological literacy, and prob-lem-solving skills as they engaged in play related to interesting topics they chose during the project-based activities. The significance of this research lies in presenting an eco-logical transition education program applied through children's expressive play with self-selected themes. The findings suggest that this approach could be utilized as a case for implementing play-centered and child-centered educational programs in early childhood education and care settings to promote ecological transition education for a sustainable society.