This research is motivated by the low quality of mathematics education in Indonesia, especially for higher order thinking skills. One learning model that can be applied to improve student's critical thinking skills is the Group Investigation (GI) and Problem Based Learning (PBL) learning model. This research was a quasi-experimental study with the design of The Static Group Pretest-Posttest Design. The population in this study were students of SMA Negeri 1 Garut. The research sample is class XI MIPA 1 who gets the Group Investigation learning model, class XI MIPA 2 who gets the Problem Based Learning learning model. The results of this study indicate that the students' mathematical critical thinking skills and the increase between those who get the Group Investigation learning model are better than the Problem Based Learning learning model.