A research on the effects of the microteaching Multiple-Representation Lesson Study (MRLS) on pre-service Physics teachers' critical thinking was conducted using a pre-test-post-test quasi-experimental design. Eighteen fourth year Bachelor of Secondary Education-Physical Science majors participated in the research. The experimental group employed the microteaching MRLS while the control group implemented the Traditional Instructional Planning Approach (TIPA). Data were gathered from multiple sources such as researcher-made written tests, interviews, diaries, and field notes. The Mann-Whitney U test was utilized to ascertain statistical difference between the experimental and the control group. Results revealed significant differences in the scores between the two groups in the overall critical thinking and on its sub-domains. Findings indicate beneficial effects of the microteaching MRLS in developing pre-service teachers' critical thinking.