Acquiring critical thinking skills is one of the important educational outcomes that need to be highly considered to help individuals succeed and cope with the challenges of living in a rapidly changing world. This research investigated the effect of using the lesson study (LS) model to improve EFL Omani teachers' ability to integrate critical thinking skills within their lessons. A case study design was used for this purpose. The sample involved five EFL Omani teachers in a government school in Oman. This case study was designed to investigate the usefulness and the challenges of introducing this model in helping teachers use teaching strategies to improve their students' critical thinking skills. This study utilized a mixed method approach. Data were collected through quantitative measures using a pre survey and a post survey. The survey was used to measure the frequency of teachers' use of critical thinking strategies before and after introducing the model. In addition, a classroom observation checklist was used by the teachers while they observed lessons. Qualitative measures including video recordings of teachers' meetings and lessons and an open-ended item in the post survey was also used. The findings of this study revealed that the frequency of teachers' use of critical thinking teaching strategies increased after engaging in the LS process. Furthermore, the teachers successfully integrated critical thinking practices as they progressed in the LS process. Further research on the effect of LS on helping EFL teachers develop students' critical thinking is recommended.