This study aims to improve students' critical thinking skills through the application of problem-based learning models based on scientific literacy in class IV. This type of research is Classroom Action Research (CAR). The class action research was carried out in 3 cycles, each cycle consisting of two meetings. This research consisted of the stages of planning, implementation, observation, evaluation and reflection. The subjects of this study were the IVB grade students of SDN 1 Tinggarjaya, amounting to 11 male students and 15 female students. Data collection tools use critical thinking skills tests, teacher activity sheets and student activity sheets. The results of the critical thinking skills test are based on five indicators of students' critical thinking skills that are carried out at each end of the meeting. The results of this class action research show that learning using the problem-based learning model based on scientific literacy can improve students' critical thinking skills on the theme of 7 Beautiful Diversity in My Country in class IVB SDN 1 Tinggarjaya. Students experience an increase in each cycle, namely, in cycle 1 an average score of 1.95 is obtained with unfavourable criteria, cycle 2 obtains an average score of 2.57 with unfavourable criteria and cycle 3 obtains an average score of 3.04 with good criteria.