Critical thinking skills (CTS) have been applied in the learning environment to address students' challenges in the twenty-first century. Therefore, specific approaches need to be implemented in the learning environment to support students' CTS. This research explores students' CTS during the learning process through the engineering design process (EDP) in a physics classroom. The methodology relied on a case study where students were situated for the first time in an EDP classroom. Data were analyzed for each of the EDP stages based on CTS criteria codes. The accuracy of the data was tested through a peer review process to demonstrate the validity of the analysis. The results showed that students exhibited specific CTS criteria in each EDP stage. Therefore, EDP could be an alternative method to engage CTS. This result contributes empirical evidence that the research on CTS also needs the students' performance while engaged in EDP.