This research aims to improve students' research skills through light diffraction experiments using the problem-based learning model. This research is included in the type of classroom action research. The research took place in two cycles. The respondents were 33 class XII Science students from SMAN 1 Tanjung. Students' research skills are reviewed in three aspects: skills in using tools, compiling reports, and presenting results. The rating scale used is a 4-point Likert rating scale. Research skills were analyzed using the Wilcoxon Signed Rank Test, stacking analysis, and racking. The results of the analysis show that there is a significant difference between students' research skills in cycles 1 and 2. After learning in cycle 2, it was identified that students to gain research skills in the low category. Of the three aspects of research skills studied, the skill of presenting results experienced the highest increase compared to the other two aspects. So, applying PBL learning through two-cycle PTK research has improved the research skills of class XII Science students at SMAN 1 Tanjung.