This study took 'context' as a focal point in the context-based approach and its investigation was anchored on an analytical framework, which is composed of three dimensions of context: origins, intentions, and occasions. Content analysis was employed as the research methodology with 878 contexts identified from 96 copies of awarded chemistry lesson plans being the analysis targets. The occurrence of context adopted in these chemistry lesson plans was analysed along the three dimensions, each of which comprises three sub-dimensions. For each dimension, content analysis focused on the proportion of three sub-dimensions, different proportions between junior and senior high schools, and the changing trends of the three sub-dimensions during the period from 2001 to 2020. As found in this study, discrepancies existed in the proportions of the sub-dimensions of origins, intentions, and occasions of context that were adopted by chemistry teachers, and some significant differences lay in chemistry teaching between junior and senior high schools. The findings are discussed against the social background in Macao, where this study took place. This study has provided several implications for the research and practice of the context-based approach in chemistry education and beyond.