Penelitian ini dilatarbelakangi oleh rendahnya kemampuan menulis teks argumentasi siswa kelas VIII SMP Negeri 1 Rantau Utara. Siswa masih mengalami kesulitan dalam merumuskan pendapat, mengembangkan alasan yang logis, menggunakan fakta sebagai bukti, menyusun struktur teks secara sistematis, serta menerapkan kaidah kebahasaan yang tepat. Penelitian ini bertujuan untuk meningkatkan proses dan hasil pembelajaran menulis teks argumentasi melalui penerapan model Problem Based Learning. Penelitian menggunakan desain Penelitian Tindakan Kelas yang dilaksanakan dalam dua siklus. Setiap siklus terdiri atas tahap perencanaan, pelaksanaan tindakan, observasi, dan refleksi. Subjek penelitian adalah 32 siswa kelas VIII SMP Negeri 1 Rantau Utara. Data dikumpulkan melalui tes menulis, observasi, dokumentasi, dan catatan lapangan. Data dianalisis menggunakan teknik deskriptif kuantitatif dan deskriptif kualitatif. Hasil penelitian menunjukkan bahwa penerapan model Problem Based Learning dapat meningkatkan kemampuan menulis teks argumentasi siswa. Nilai rata-rata siswa pada kondisi awal sebesar 66,28 dengan ketuntasan klasikal 34,38%. Pada siklus I, nilai rata-rata meningkat menjadi 74,69 dengan ketuntasan klasikal 65,63%. Pada siklus II, nilai rata-rata mencapai 83,16 dengan ketuntasan klasikal 90,63%. Peningkatan juga terlihat pada keaktifan siswa dalam mengidentifikasi masalah, mengumpulkan informasi, berdiskusi, menyampaikan pendapat, dan memperbaiki teks berdasarkan umpan balik. Dengan demikian, model Problem Based Learning efektif digunakan untuk meningkatkan kemampuan menulis teks argumentasi siswa kelas VIII SMP Negeri 1 Rantau Utara. This study was motivated by the low proficiency in writing argumentative texts among eighth-grade students at SMP Negeri 1 Rantau Utara. Students struggled to formulate opinions, develop logical arguments, use facts as evidence, organize text structure systematically, and apply appropriate linguistic conventions. The study aimed to improve the process and outcomes of argumentative text writing instruction through the implementation of the Problem-Based Learning model. A Classroom Action Research design was employed, conducted over two cycles. Each cycle comprised stages of planning, action implementation, observation, and reflection. The research subjects were 32 eighth-grade students at SMP Negeri 1 Rantau Utara. Data were collected through writing tests, observation, documentation, and field notes, and were analyzed using quantitative and qualitative descriptive techniques. The results indicate that implementing the Problem-Based Learning model improved students' argumentative writing skills. The initial average score was 66.28, with a classical mastery rate of 34.38%. In Cycle I, the average score rose to 74.69, with a classical mastery rate of 65.63%. In Cycle II, the average score reached 83.16, with a classical mastery rate of 90.63%. Improvements were also observed in student engagement regarding problem identification, information gathering, discussion, opinion expression, and text revision based on feedback. Thus, the Problem-Based Learning model is effective for enhancing the argumentative writing skills of eighth-grade students at SMP Negeri 1 Rantau Utara.