Research in the area of educational technology has claimed that Web technology has driven online pedagogy such that teachers need to know how to use Web technology to assist their teaching. This study provides a framework for understanding teachers' Technological Pedagogical Content Knowledge-Web (TPCK-W), while integrating Web technology into their pedagogical practice. Furthermore, contemporary educational researchers have highlighted the significance of teachers' self-efficacy, conceptualized as the teachers' perceptions of their own competence at teaching, and related to instructional strategies as well as teaching effectiveness. The major purpose of this study was to investigate teachers' perceived self-efficacy in terms of their TPCK-W. This study aimed to develop a new questionnaire, namely the Technological Pedagogical Content Knowledge-Web (TPCK-W) Survey to explore teachers' self-efficacy in terms of their TPCK-W, and additionally to assess their attitudes toward Web-based instruction. The participants in this study were 558 teachers from elementary school to high school level in Taiwan. Both exploratory and confirmatory factor analyses indicated that the TPCK-W survey developed in this study has satisfactory validity and reliability characteristics. The results indicate a lack of general knowledge about Web-related pedagogy amongst the teachers surveyed. The correlations between teachers' self-efficacy in terms of their TPCK-W, their attitudes regarding Web-based instruction, and their background variables were also examined. Correlations were found between self-efficacy and positive attitudes to web-based instruction. Older and more experienced teachers were found to have lower levels of self-efficacy with respect to TPCK-W, though teachers with more experience of using the web (including for instruction) had higher levels of self-efficacy with respect to TPCK-W.