In this study, pre- and in-service preschool teachers' science teaching efficacy beliefs were investigated. The sample included 100 pre-service (50 first grades and 50 last grades) and 73 in-service preschool teachers. As a data collection tool "Science Teaching Efficacy Belief Instrument" was used. Findings indicated that in-service teachers had higher science teaching efficacy belief score than pre-service teachers. Also, last grade pre-service teachers had higher science teaching efficacy belief score than first grade pre-service teachers. Moreover, pre-service teachers who graduated from mathematics and science departments at high school had more science teaching efficacy belief score than those who graduated from literature and mathematics department. Finally, teachers who have teaching experience of more than 10 years had higher level of science teaching efficacy beliefs than those who have less teaching experience.