Abstract: This study is a classroom action research that aims to improve student’s critical thinking skills through the application of problem based learning model. This research was conducted during three learning cycles. Data collection technique used in research is observation and test. Data analysis used is quantitative descriptive analysis. The results showed that the use of problem-based learning model can improve the critical thinking skills of grade 5 primary school students. The results of the study include student activity on the first cycle reached the percentage of 66.50% while in the second cycle reached 83.75% and in the third cycle reached 88.75%; student’s critical thinking ability in the first cycle reached 55.56% percentage while in cycle 2 reached 70.37% and on the third cycle reached 85.29%. It can be concluded that the use of problem-based learning model can improve the critical thinking skills of grade 5 primary school students.