This study aims to describe the implementation of the Problem Based Learning (PBL) model and to determine the improvement of reading interest among fourth-grade students at MIS Muhammadiyah Cece. The study was motivated by the students' low reading interest, marked by weak reading habits, low reading motivation, and limited involvement in reading activities during Indonesian language lessons. This research used Classroom Action Research (CAR) conducted in two cycles, each consisting of planning, action, observation, and reflection. The subjects were 17 fourth-grade students, consisting of 10 female and 7 male students. Data were collected through observation, questionnaires, and documentation, then analyzed descriptively and quantitatively by calculating the percentages of learning implementation, student activity, and reading interest in every cycle. The results showed that the implementation of PBL improved students' reading interest. In Cycle I, only 30% of students reached the mastery criterion, with student activity at 74% (active category) and learning implementation at 83% (very good category). In Cycle II, reading interest increased to 82%, exceeding the success indicator of at least 75% of students scoring ≥80, while student activity and learning implementation both reached 96% (very active and very good). It is concluded that the PBL model is effective in improving fourth-grade students' reading interest at MIS Muhammadiyah Cece.