Natural science subjects in elementary schools are adapted based on student growth so that the students create their own knowledge and concepts through everything that they learn in nature. The study aimed to describe the steps of problem-based learning based on socio-scientific issues, analyze the improvement of critical thinking, and examine student responses in natural science. It was classroom action research. The results indicated that the teacher performance in problem-based learning based socio-scientific issues reached 91% of the research performance indicator the minimum indicator was 80%, the improvement of critical thinking achieved 89%, and student responses reached 89%. It concludes that problem-based learning based on socio-scientific issues improves critical thinking if it is implemented correctly.