This research is a research that uses a qualitative approach, because researchers want to obtain in-depth data naturally about students' metacognitive skills in solving mathematical problems. Meanwhile, this type of research is descriptive research that will describe/explain how students' metacognitive skills emerge during the mathematical problem solving process. The research data was obtained through the results of solving mathematical problems which were carried out in writing in groups, the results of think a loud and the results of interviews. The results showed: a) The students' metacognitive skills in problem solving planning activities looked good. This is shown from a good understanding of mathematical problems by students to further plan problem solving, b) Students' metacognitive skills in monitoring activities look quite good. students produce different answers due to the collection of information for problem solving that students have is not the same and some are lacking/wrong, and c) students' metacognitive skills in evaluation activities look good. From the two different answers, the students jointly re-examined by adjusting the Venn diagram with the main statement in the given mathematical problem.