Research attention to investigating elementary STEM teachers' Professional Learning Networks (PLNs) has grown. However, what types of Open Educational Resources (OER) and Technological, Pedagogical, and Content Knowledge (TPACK) elementary STEM teachers share in their PLNs are still under-examined. This case study aims to explore elementary STEM teachers' use of OER, types of TPACK, and their relationships. Using qualitative content analysis, we analyzed qualitative messages extracted from a Facebook community for elementary STEM teachers. The results showed that tools and tips were the most commonly shared among the various OER types, and technology-related knowledge (i.e., TK and TPK) emerged dominant within the PLN. Also, we discuss the implications of elementary STEM teachers' discourses on OER and TPACK in a PLN. [Note: The page range (192-213) shown on the PDF is incorrect. The correct page range is 192-215.]