Wiki bears great potential to transform learning and instruction by scaffolding personal and social constructivism. Past studies have shown that proper application of wiki benefits both students and teachers; however, few studies have integrated wiki and collaborative learning to examine the growth of science teachers' "Technological, Pedagogical and Content Knowledge" (TPACK). This study introduced a wiki-based TPACK growth model and examined nine elementary and middle science teachers' knowledge growth in a graduate-level course. Data sources included reflective journals, wiki data and interviews. Results showed that with wiki, science teachers learned to design more understandable and lively science teaching content, and they collaboratively generated creative instructional strategies. Furthermore, wiki and collaborative learning helped in-service teachers exchange and elaborate ideas related to the development of TPACK. Implications, suggestions and future research directions were put forward regarding wiki, TPACK and in-service teachers' professional development.