Teachers' high quality questions encourage students' scientific observations and promote students' investigations in science activities. In particular, open-ended questions enhance students' higher skill thinking and help them actively express their ideas. However, previous studies report that most teachers do not use open-ended questions frequently in practice and instead rely on low quality questions eliciting simple piece of information or managing students' behaviors. Therefore, in order to improve teachers' questioning, it is necessary to provide teachers with appropriate professional development. This study involves implementing blended professional development to enhance teachers' use of open-ended questions. Based upon social cognitive theory and experiential learning theory, blended professional development offers models of teachers' high quality questioning strategies and promotes teachers' reflective thinking upon their own practice. It provides questioning demonstration videos and questioning tips through online professional development website and face-to-face workshops to help teachers practice questioning strategies and analyze their questioning practice. As a result, treatment group teachers asked significantly more open-ended questions than control group teachers. Moreover, treatment group teachers significantly increased their use of open-ended questions in the middle and end of the academic year than in the beginning of the academic year.