Jejudo Island’s sustainable urbanisation journey offers a compelling narrative that distinguishes its cultural heritage from the broader South Korean experience. This paper investigates the intersection of Indigenous knowledge, cultural practices, and sustainable urban development in Jejudo Island during the phase 1946~1970. Unlike the rapid industrialisation of mainland South Korea, Jejudo Island’s development has been shaped by geographic isolation, harsh environmental conditions, and a smaller population. These factors have preserved unique traditions, such as the Jejuuh dialect, Haenyeo (female divers), and Dottongsi (pig latrine systems), which reflect a deeply rooted harmony between human activity and the natural environment. The study employs a mixed-method approach, including content analysis of archival data and a questionnaire survey of 330 Jeju Special Self-Governing Province officials. Findings reveal widespread awareness of Jejudo Island’s cultural practices and their perceived contributions to economic, social and environmental sustainability. Senior officials strongly support preserving these traditions, underscoring the need to engage younger generations through targeted education and community initiatives. A core distinction between Jejudo Island and mainland South Korea lies in the island’s reliance on communal labour-sharing systems (Sunureum), collective social networks (Gwendang), and ritualistic respect for nature (Singugan). These practices exemplify Jejudo Island’s cultural resilience and self-reliant development model, which contrasts with South Korea’s top-down, growth-centric urban strategies. The research advocates for integrating Indigenous knowledge into urban planning frameworks, aligning with Sustainable Development Goal 11 (Sustainable Cities and Communities). Jejudo Island stands as a model for balancing modernisation with preserving intangible heritage, offering lessons for sustainable urbanisation globally.