The purpose of this study was to examine the differences in the improvement of students' critical thinking skills between students who received treatment using the MIKiR-based STEM learning approach and students who only used conventional learning at the 191 Pekanbaru State Elementary School in science learning material energy sources. The research method used is a quantitative research method that uses an experimental design using 2 classes as the control group and the experimental group. Each class will be given a pre-test before being given treatment and a post-test given treatment. The results showed that there was a significant effect of the application of MIKiR-based STEM learning on the critical thinking skills of fourth grade students at SDN 191 Pekanbaru in science learning where the significance value was 0.000 <0.05. Therefore, it can be said that there is a significant effect on the application of MIKiR-based STEM learning on students' critical thinking skills on energy source materials.