This study aims to investigate the implementation of Realistic Mathematics Education (RME) approach based on Lesson Study for Learning Community (LSLC) as an effort to improve students' mathematics understanding. The research method used was classroom action research involving 21 students of grade VII of SMP Negeri 1 Arjasa Kalinganyar Sumenep Madura. This research consists of two implementation cycles, where each cycle consists of planning, implementation, observation, and reflection with three instruments, Open Class Observation, tests and documentation. The results of this study indicate that the implementation of LSLC-based RME is able to have a positive impact on student understanding. Data analysis showed an increase of 20% seen from open class and an increase of 31% from the test results. This research shows that the LSLC-based RME approach can be an effective alternative in improving the quality of mathematics learning in the classroom. Collaboration between teachers and curriculum development that focuses on realistic concepts in mathematics make an important contribution in strengthening students' understanding. The implication of this finding is that the application of this approach should be considered in the effort to improve mathematics learning in schools.