This study aims to improve the understanding of 5th-grade students at SDN Tawangrejo regarding the concept of changes in the states of matter through the implementation of Problem-Based Learning (PBL). PBL is used as a learning approach that encourages students to actively seek solutions to given problems. The study involved 18 5th-grade students as research subjects. The research adopted the Classroom Action Research (CAR) approach, consisting of four stages: planning, action, observation, and reflection. During the action stage, the teacher introduced the concept of changes in the states of matter through relevant real-life problem scenarios. The students were then assigned to work in groups, analyze the problems, gather information, and develop solutions. This process was supported by facilitation and guidance from the teacher. The results of the study show that the implementation of PBL significantly improves students' understanding of the concept of changes in the states of matter. There is a significant improvement in students' ability to identify changes in the states of matter, understand the factors influencing these changes, and explain the process of changes in the states of matter more comprehensively. Additionally, the students demonstrated more active participation in the learning process and improved teamwork skills. This research recommends that teachers and schools utilize the PBL approach in teaching the concept of changes in the states of matter. The implementation of PBL can enhance students' understanding and facilitate the development of collaboration and problem-solving skills. The study also emphasizes the importance of connecting learning to everyday life contexts to help students recognize the relevance of the material being taught
 Keywords: Increased understanding, Concept of changes in states of matter, PBL (Problem Based Learning)