In this research, it is aimed to develop a valid and reliable measurement instrument that will enable teachers to measure the inquiry-based teaching self-efficacy for STEM+S education. The research was conducted on 535 teachers who actively pursued their profession in the schools affiliated to the Ministry of National Education in different regions of Turkey in March-April-May 2017. For the face and content validity of the scale, expert opinion was applied and Explanatory Factor Analysis (EFA) and Confirmatory Factor Analysis (CFA) were applied for the validity of the scale. As a result of EFA, a structure consisting of 17 items and four factors explaining 62.72% of the total variance was obtained. The emerging factors; discussion and reflection, investigate and creation, asking and relation with daily life. Findings from the CFA show that the inquiry-based teaching scale structure is containing 17 items and 4 dimensions has good indices. The reliability of the measurement tool was examined in terms of consistency and stability. The Cronbach's alpha reliability coefficients for the subscales of discussion and reflection, investigate and creation, asking and relation with daily life were found to be .85, .80, .73 and .69, respectively. Based on these findings, it can be said that this scale is a valid and reliable measurement tool that can be used to measure the inquiry-based teaching self-efficacy for STEM + S education.