The development of the times, the teaching and learning process is required to be more innovative in order to spur student activeness. However, this is still difficult to achieve, one of which is due to the lack of student participation and enthusiasm in asking questions which is one indicator of the low ability to think in students. To stimulate student activeness while learning, the Group Investigation type cooperative learning model is used. The purpose of this study was to determine the effect of the Group Investigation (GI) Cooperative learning model on critical thinking skills in fifth grade students at SDN Tegalsari. The research method used was a quantitative approach with a pre-experimental one group pretest-posttest research design. The results showed an increase in critical thinking skills in students after the application of the learning model. This is evidenced by the results of data analysis calculations with an average N-Gain score of 0.6101 which means it shows moderate criteria in improving ability.