This study aims to systematically investigate the insect diversity within the distinct coastal grassland and mountain habitats of East Busan, Busan Metropolitan City. The objective is to gather foundational data that will inform natural environment conservation plans and contribute to policy formulation. Employing a comprehensive collection approach, we utilized trapping nets, pitfall traps, and flying insect traps to capture a broad spectrum of insect species. The investigation identified a rich diversity of 132 species across 9 orders and 52 families. Coleoptera emerged as the most prevalent order with 13 families and 41 species, followed by Diptera with 8 families and 24 species, and Lepidoptera with 9 families and 21 species. To assess the biodiversity and structure of these communities by habitat type, we applied several biodiversity indices: the Shannon-Wiener index (H'), Margalef index (R), and Pielou evenness index. Coastal grasslands exhibited an H' of 3.153, R of 11.08, and a Pielou evenness of 0.371; coastal mountains showed an H' of 2.922, R of 13.02, and a Pielou evenness of 0.202. These metrics reveal no significant differences in diversity and evenness between the two habitats. The endangered Copris tripartitus was notably observed in coastal grasslands, alongside 20 species classified as Least Concern (LC) in the National Red List across both habitats. The comparative analysis of biodiversity and evenness levels across coastal grassland and mountain areas highlights the ecological significance of both habitats in supporting a diverse insect fauna. The detection of endangered and LC species within these areas emphasizes the critical need for ongoing monitoring and the development of effective conservation strategies tailored to protect Busan's coastal ecosystems. The findings underscore the necessity of conducting periodic surveys to monitor faunal changes and inform conservation efforts actively. By ensuring the continued protection of insect diversity, these efforts will play a pivotal role in maintaining the ecological integrity of coastal areas, thereby supporting broader environmental conservation objectives.