This study examined how ocean education at two elementary schools in northwestern Tsushima City, Nagasaki Prefecture, deepened children’s understanding of local history and biodiversity. Tsushima, situated between Japan and the Korean Peninsula, boasts of rich historical backgrounds and diverse marine ecosystems. Students at Toyo Elementary School and Sasuna Elementary School participated in experiential learning activities, including studying local historical sites, interviewing fishermen, and observing marine organisms. Through these activities, they came to understand that their local ports once served as relay points for diplomatic envoys such as the Joseon Tongsinsa. Furthermore, through fishery surveys and organism rearing, students developed a greater awareness of species diversity and ecosystem interconnections. Ocean education that integrates local history and biodiversity enhances students’ scientific and historical knowledge and fosters recognition of the value of their own environment and cultural heritage. This study aligns with the concept of Education for Sustainable Development (ESD) as promoted by the Japanese national curriculum guidelines.