Teacher training is a necessary prerequisite for the effective teaching of engineering. When introducing teachers to engineering, teachers must deal with contents, materials, and teaching styles different from other subjects. Under these circumstances, many professional development programs that teamed up universities have been developed and applied for teachers to be qualified and confident in teaching engineering. Although a lot of efforts have been focused on teacher education, there has been no credible instrument developed to measure teachers’ self-efficacy in teaching engineering. This project is to develop and validate the TESS to measure teachers’ engineering teaching self-efficacy. For this study, engineering teaching self-efficacy was defined as teachers’ personal belief in their ability to positively affect students’ learning engineering. Thus, the use of the TESS, as a teacher self-efficacy instrument tailored for the engineering teaching context, is expected to serve to diagnose and clarify the teacher’s self-efficacy system and to further understand teachers’ behavior in class.