Teaching Natural Science subjects in grade 6 at Secondary schools can be understood as the process of impact of teachers teaching Natural Science subjects on grade 6 pupils, through educational activities, to impart knowledge of Natural Science, to achieve academic objectives according to the regulations of the general education program. Studies have shown that teaching Natural Science subjects in grade 6 at Secondary schools is designed to develop the qualities and abilities of Natural Science for grade 6 pupils. This educational activity has achieved some positive results in the past but still reveals some limitations. Exploring theoretical issues in teaching Natural Science subjects in grade 6 at Secondary schools will help identify necessary content and orientation for practical activities. Based on the assessment of legal documents of the state; research selectively inherits in-depth research of several researchers; analyze, compare, synthesize, and evaluate; this study has discovered theoretical issues on teaching activities of Natural Science subjects in grade 6 at Secondary schools as position, role, objectives, content, methods, forms as well as conditions to ensure teaching activities of Natural Science subjects in grade 6 at Secondary schools. Discovering these contents has clarified and supplemented the missing content on theoretical issues; at the same time, it is the basis for applying to educational practice at Secondary schools.