It was aimed to investigate the relationship between collective efficacy and science teaching efficacy beliefs of pre-service teachers. The study was composed of four junior pre-service science teachers working together to fulfill the tasks of a science methods course. They were interviewed at regular intervals during one semester. The results revealed that the sources of collective efficacy played an essential role in the development of personal science teaching efficacy and science teaching outcome expectancy of the group members. The participants most emphasized the effect of the positive influence of mastery experience. It was concluded that science teacher educators could consider collective efficacy when designing their courses to improve pre-service teachers' science teaching efficacy beliefs.