Helping students at all grade levels to develop inquiry skills has been an ambitious goal that science educators have been pursuing for the last three decades. Yet, studies consistently report cases of failure from science classrooms with regard to inquiry-based teaching. The purpose of this study was to develop an instrument for measuring primary teachers' self-efficacy to teach science through inquiry. An expert panel methodology was used to develop and validate the initial instrument. The final, and thus administered survey consisted of 29 Likert-scale questions. To further validate and develop the instrument, we collected data from 358 pre-service primary teachers enrolled in teacher education programs at five different universities in Turkey. According to exploratory factor analysis, there is only one interpretable factor. Cronbach's alpha internal consistency coefficient was found to be 0.97 for the reliability, indicating the robust scale reliability. We present the need for such an instrument and evidence on the validity and reliability of the instrument. We further discuss the potential contributions of this instrument to the field.