Researchers have proposed that to foster epistemological development, students should engage in the discussion of controversial issues, conduct open-ended inquiry projects, discuss, and analyze ill-structured problems, work on group learning, peer interactions or so-called constructivist-based instructional activities. Clearly, the Internet-based learning environments contain rich information and a variety of perspectives and viewpoints for inquiry exploration or the debates of controversial issues. They also allow numerous ways of group learning and peer interactions, either synchronous or asynchronous. The purpose of this study was to investigate a group of Taiwanese high school students’ epistemological development by involving in some Internet-based inquiry learning activities in science. The students were asked to find more online information to explore scientific knowledge taught in science class further. Also, they were requested to search Internet information to resolve some controversial issues, and they were allowed some opportunities to participate in some online discussions and debates. Students’ standards of evaluating online information and their epistemological beliefs toward science were probed before and after the treatment instruction by using questionnaires. Through comparing the students’ responses, it was found that their judgmental standards of assessing online information became more sophisticated, and their epistemological beliefs toward science, in some aspects, were enhanced. Some of the findings were interpreted through a cultural lens. Future research issues were also discussed.