This study aims to develop a learning model based on 4C skills to improve high school students' mathematical critical thinking skills. Research & development is the design used in this research by applying Plomp's development theory which consists of three phases, namely needs analysis, design and implementation, and evaluation. This research was conducted at Madrasah Aliyah Negeri 2 Parepare, South Sulawesi, Indonesia involving five experts, four teachers, and 20 students. Data collection and analysis were carried out qualitatively and quantitatively. Analysis of interviews' data and observations qualitatively with the thematic analysis technique. We also analyse data from validation sheets, questionnaires, and mathematical essay tests with the help of SPSS 20.00. The results show that students and lecturers need a learning model to improve mathematical critical thinking skills. In addition, other findings stated that the learning model developed was proven to be valid, practical, and effective to be used in general. Developing your learning model can further improve students' learning outcomes and mathematical critical thinking skills because they are designed based on the actual needs and problems. For this reason, a teacher must be able to design his learning model.