So far, elementary schools have found problems with students' critical thinking skills, which could be improved by implementing thematic learning, so a learning model is needed to train students' critical thinking skills. The purpose of this study was to analyze whether there were differences in the level of effectiveness of the Problem-Based Learning model in improving critical thinking skills in thematic learning of students in grade IV SD/MI, namely SDN II Weringinanom Poncokusmo Malang, East Java, Indonesia. This type of research is Classroom Action Research using qualitative and quantitative approaches. The subjects used in the study were class IV teachers and 46 students. The results showed an increase from cycle I to cycle II. The implementation of the teacher cycle I was 80.73%, increasing to 91.76% in cycle II and 85.09%, increasing to 92.96% in cycle II on student implementation. Thus, the Problem-Based Learning model has improved integrated thematic learning in fourth-grade students at SD SDN II Weringinanom Poncokusmo Malang, East Java, Indonesia.