Inquiry is the core of modern science education. In science classes, conducting science fair projects is one of the most common inquiry activities. Through conducting these projects, learners have the chance to carry out open inquiry which may help them build deeper understanding of science knowledge, concepts, science skills, and positive attitudes toward science. However, previous research has revealed that teachers encountered many challenges when implementing inquiry-based instruction, such as insufficient time, sources, professional knowledge and experience of inquiry learning. To address the important issue, by integrating community-based knowledge management (KM) tools and personal-based knowledge management (PKM) tools, a KM-based online teacher community platform was developed and preliminarily evaluated in this study. Moreover, cluster analysis was also conducted to categorize the participants' attitude-behavior patterns into different clusters, and the attitudes and behaviors of these different clusters were further analyzed. A total of 103 volunteer Taiwanese elementary school science teachers participated the system evaluations of the Teacher Science Fair Instruction Knowledge Management System (TSFI-KMS) in this study. Their responses on the quantitative questionnaire designed for the system evaluation in this study showed that they expressed satisfactory perceived usefulness and ease of use of the TSFI-KMS. Also, they expressed high willingness to use the TSFI-KMS for professional development regarding inquiry-based instruction. Further analysis indicate that the teachers' perception and usage preference toward TSFI-KMS might be influenced by their academic background and experience of using social media. In this study, suggestions on teaching practices, improvement on the system design, and future research are also discussed.