This study examines the Problem Based Learning (PBL) model in enhancing the critical reasoning skills of fourth-grade students in Indonesian language learning at UPT SPF SD Inpres Gunung Sari Baru. The research problem focuses on how the application of the Problem Based Learning model improves students' critical reasoning skills in Indonesian language learning in the fourth grade at UPT SPF SD Inpres Gunung Sari Baru. The objective of this study is to describe the implementation of the Problem Based Learning model in enhancing the critical reasoning skills of students in Indonesian language learning in the fourth grade at UPT SPF SD Inpres Gunung Sari Baru. This Classroom Action Research uses the Kemmis & McTaggart model. Data collection techniques include observation, tests, and documentation. Data analysis uses data condensation, data presentation, and conclusion drawing. In Cycle I, the process includes planning, which involves identifying problems, setting goals, and planning actions. The actions taken involve using the PBL model, providing worksheets and relevant problems. Observation is conducted during the action process to observe the learning process of teachers and students using the PBL steps and to collect observational data. The next stage is reflection, which aims to evaluate and conclude students' critical reasoning abilities using tests. In this stage, it is observed that there are aspects that need improvement and the determination of the next steps. The results of the study show that in Cycle I, the teacher observation results fall into the less satisfactory category, and the student observation results also fall into the less satisfactory category or have not yet reached the success standard. Meanwhile, the results of students' critical reasoning tests in Cycle I are in the low criteria or it can be said that many students have not yet met the success standard. In Cycle II, the planning stage involves identifying problems based on the results of Cycle I, setting goals, and planning actions. During the action stage, the PBL model is used, and relevant worksheets and problems are provided. Observation is conducted during the action process to observe the learning process of teachers and students using the PBL steps and to collect observational data. The reflection stage uses evaluation tests to evaluate and conclude students' critical reasoning abilities. As a result, the teacher observation results in Cycle II fall into the good category, and the student observation results in Cycle II also fall into the good category or have reached the desired success standard. The results of the students' critical reasoning tests in Cycle II show that the researcher succeeded in enhancing the students' critical reasoning abilities to a very high criterion.