The student-centered learning approach is in line with the development of information technology. In this case students must be provided by various things for establishing critical thinking skills. Those critical thinking abilities were built with the use of Problem-Based Learning (PBL) with Brainstorming techniques. The purpose of this study was to develop the students' critical thinking skills in Natural Science learning through PBL models with Brainstorming techniques. This study used a qualitative method with a grounded theory approach. The validity of the data included: credibility; transferability; dependability, and confirmability. The data analysis techniques used was the Miles and Huberman Model which included: data collection, data reduction, data display, and verification. The respondents were fifth grade students at SDN 01 Mandiraja Pemalang. The data collections techniques used were observation, questionnaires, interviews, and documentation. The results showed that Brainstorming techniques of PBL learning model made the students had critical thinking skills.