<p>International science education documents have advocated that the requirements of nature of science (NOS) should be gradually deepened as the grade level increases. Employing the framework of the family resemblance approach (FRA) to nature of science (NOS), this study innovatively examined the changes of NOS frequencies and connotations in chemistry textbooks across different school stages, under the context of Chinese curriculum reform. Data sources consisted of Chinese junior high school, and senior high school compulsory and selective chemistry textbooks, respectively designed for Grade 9, 10 and 11 students. The results indicated that there were differences regarding NOS representations in chemistry textbooks at different school stages. Specifically, compared to junior ones, senior high school chemistry textbooks involved NOS categories with a larger quantity and richer connotations. However, no progressions of NOS representations were found from senior high school compulsory to selective chemistry textbooks, as both exhibited similar NOS frequencies and connotations. Finally, explanations for the results, implications of the findings, and suggestions for future research were discussed.</p>