Metacognitive skills are very important for every student in improving understanding and effective problem-solving. This study aims to enhance students' metacognitive skills through a problem-based learning model in biology in class X.10. The sample for this study was class X.10, selected due to lower student understanding compared to other courses. The research method is PTK (Classroom Action Research). The PTK method was carried out over two cycles to assess improvements in students' metacognitive skills. Students' metacognitive skills were measured using essay questions from the pretest and posttest, integrated with the metacognitive skills rubric. The study found an increase in students' metacognitive skills. The increase in students' metacognitive skills is evident in the N-Gain scores: cycle I 0.37 in the low category, and cycle II 0.80 in the medium category. This shows that implementing the PBL learning model improves students' metacognitive skills, as it trains them to understand and solve problems.