The aim of this research is to improve the critical thinking skills of students of class XI High School of Mathematics and Science through the implementation of Constructivist-Metacognitive Model in material coordination system. This research is a classroom action research conducted in two cycles, from February to April 2016. Each cycle consisted of four stages, i.e. planning, action, observation, and reflection, in accordance with the procedures of Mc.Taggart Kemmis. The subjects were 32 students of class XI SMA who choose specialization in Mathematics and Science. Indicators of students' critical thinking skills is the ability of interpretation, analysis, evaluation, inference, explanation and self-regulation, which is measured using a test instrument essay. Data furnished by the observation of learning activities and interviews with students and teachers. Data analysis techniques used descriptive analysis techniques. The target of this research is to increase the capability of critical thinking by 30% from the base line. The results showed the application of Constructivistl-Matakognitif Model can improve students' critical thinking skills research participants. Initial profile of students' critical thinking skills by 22.53% with the low category. Critical thinking skills first cycle of 49.08% with category but do not meet the target of research. Critical thinking skills in the second cycle of 62.89% with a high category and has met the target of research.