ABSTRAK Permasalahan yang melatarbelakangi penelitian ini adalah rendahnya hasil belajar siswa pada pembelajaran matematika siswa kelas 3 SDN rungkang 02, Kabupaten Brebes. Penelitian ini menggunakan penelitian tindakan kelas yang dilaksanakan dalam 2 siklus. Masing-masing siklus dilaksanakan dalam 4 (empat) tahap, yaitu perencanaan, implementasi, observasi, dan refleksi. Subjek penelitian ini adalah siswa kelas 3 SDN rungkang 02 yang berjumlah 25 orang. Instrumen yang digunakan dalam peneltian ini adalah tes, observasi, dan dokumentasi. Teknik analisis datanya menggunakan analisis deskriptif kualitatif dan kuantitatif. Berdasarkan hasil penelitian dapat disimpulkan bahwa pembelajaran dengan model Problem Based Learning dapat meningkatkan hasil belajar pada mata pelajaran matematika materi bilangan cacah. Hasil sebelum dilakukan tindakan yaitu pada pra siklus hanya 8 siswa atau 32% yang tuntas, pada siklus I meningkat menjadi 17 siswa atau 68% yang tuntas belajar matematika dan pada siklus II meningkat lagi menjadi 23 siswa yang tuntas belajar matematika atau 92%. Penelitian ini dikatakan berhasil karena mencapai indikator kinerja yaitu ≥ 80% dari seluruh siswa dengan KKM ≥ 70. Kata kunci: Hasil Belajar, Matematika, Problem Based Learning. APPLICATION OF PROBLEM BASED LEARNING (PBL) LEARNING MODEL TO IMPROVE MATHEMATICS LEARNING ACHIEVEMENT IN GRADE III STUDENTS OF SDN RUNGKANG 02 ABSTRACT The problem behind this research is the low student learning outcomes in mathematics learning for grade 3 students at SDN Rungkang 02, Brebes Regency. This research uses classroom action research carried out in 2 cycles. Each cycle is carried out in 4 (four) stages, namely planning, implementation, observation and reflection. The subjects of this research were 25 grade 3 students at SDN Rungkang 02. The instruments used in this research are tests, observation and documentation. The data analysis technique uses qualitative and quantitative descriptive analysis. Based on the research results, it can be concluded that learning using the Problem Based Learning model can improve learning outcomes in mathematics subjects involving whole numbers. The results before action was taken were that in the pre-cycle only 8 students or 32% had completed it, in the first cycle it had increased to 17 students or 68% who had completed studying mathematics and in the second cycle it had increased again to 23 students who had completed studying mathematics or 92%. This research was said to be successful because it achieved a performance indicator of ≥ 80% of all students with a KKM ≥ 70. Keywords: Learning Outcomes, Mathematics, Problem Based Learning.