This study analyzes the elements of the nature of science (NOS) with respect to environmental issues in middle-school science textbooks, covering three collections (nine and 12 books) from South Korea and Brazil, respectively. Content analysis was used to categorize the elements of the NOS using the reconceptualized family resemblance approach to the NOS (RFN) framework. The results showed that middle-school science textbooks mentioned the NOS when discussing environmental issues. The Brazilian textbooks mentioned RFN categories more often than the South Korean textbooks (103 vs. 24). Specifically, professional activities were the most mentioned RFN category in the Brazilian textbooks (32, 31.1%), while social values (6, 25%) were most mentioned in the South Korean textbooks. Additionally, the categories of aims and values (2, 1.9%), scientific ethos (1, 1.0%), and political power structures (4, 3.9%) were present in the textbooks from Brazil but not in those from South Korea. The financial system category was not identified in the textbooks of either country. Notably, most mentions of RFN categories in the textbooks were implicit in nature and did not have in-depth descriptions. Based on these results, this study discusses how exploring the general principles of the NOS and its specific applications in environmental issues can promote the role of science textbooks in environmental education. Further, the study findings contribute to clarifying the differences between South Korea and Brazil regarding environmental issues associated with the NOS, indicating that both countries can learn from each other's perspectives on environmental education and the NOS.