The purpose of this community service activity is to improve the critical thinking skills of grade IV students at SD Negeri Johar Baru 15 through the application of a problem-based learning model. This activity was carried out 2 times, namely on 29 August 2022 and 12 September 2022. All 23 grade IV students participated in the activity. The implementation method includes five steps: 1) Orientation of students to the problem; 2) Organizing students to learn; 3) Guiding investigations; 4) Develop and present the work; 5) Analyse and evaluate the problem solving process. Critical thinking skills include four indicators: 1) Formulating problems; 2) Disclosing facts; 3) Give arguments; 4) Think inductively. Critical thinking ability data is obtained by administering a test at the end of each meeting. The results of the activity show that the indicator for formulating a problem at meeting 1 gets a score of 72, increasing at meeting 2 to 90; The indicator for disclosing facts at meeting 1 scored 68 and increased at meeting 2 to 86; For indicators giving arguments at meeting 1 getting a value of 70 increases at meeting 2 to 81; The inductive thinking indicator increased from 74 to 86. Thus it can be concluded that the application of the problem-based learning model has improved the critical thinking skills of fourth grade students at SD Negeri Johar Baru 15