This study aims to analyse the effects of science teaching practices supported by Web 2.0 tools on prospective elementary school teachers' perceptions of self-efficacy beliefs in using Web 2.0 tools. The study was conducted in pre test-post test quasi-experimental design with no control group, and it was supported with qualitative data. The research was conducted with the participation of 40 prospective teachers registered in Elementary School Teaching Department of a state university in 2017-2018 academic year. The study was conducted throughout a semester (for 14 weeks) within the scope of the course Science and Technology Teaching II. The lessons were taught in consistence with constructivist learning approach directed to all the gains available in the 3rd and 4th grade Science teaching curriculum prepared by the Ministry of National Education (MNE) (2018) on the basis of student-centred methods and techniques by supporting with Web 2.0 tools. 23 Web 2.0 tools in total were used throughout the study. The "Web 2.0 Rapid Content Development Self-efficacy Scale" developed by Birisci, Kul, Aksu, Akaslan and Çelik (2018) in addition to an interview form of openended questions developed by the researcher to obtain prospective teachers' views on the use of Web 2.0 tools in science teaching were used in this study. Consequently, it was found that science teaching practices supported by Web 2.0 tools had positive effects on prospective elementary school teachers' their self-efficacy perceptions on the use of Web 2.0 tools. An examination of the participants' responses to the open-ended questions demonstrated that the participants said that Web 2.0 tools had positive impacts especially on the learning process and they were innovative and they improved upper order thinking skills, creativity and imagination and that they could be used especially in eliminating the anxiety and misconceptions in science teaching.