This study explains the effect of discovery learning on the mastery of the ecosystem concept in terms of student activity. The study was conducted on SDN 135 Salebbo Mario South Sulawesi with 34 students. This research uses an experimental method with a quasi-experimental design using a pretest-posttest control group. Obsessive sheets are used to measure student activity after the learning process, and multiple choice tests are used to measure the level of mastery of ecosystem concepts. The results of discovery learning and learning in the environment have an impact on the ecosystem concept. There is an influence of student activity on mastering the ecosystem concept. There is an interaction between discovery learning and activity to master the ecosystem concept.