The paper reports on a collaborative project on fostering cross-cultural online discussion between two universities with one in Hong Kong and the other in Taiwan. Two online platforms—Moodle as a formal channel for course-related discussion and Facebook as an informal channel for social-oriented interaction—were employed. The study pays special attention to instructional design based on research-derived strategies and reflects on the effects of various strategies as well as students’ experiences and perceptions. The results show that the students perceived the online discussion as valuable for exchanging perspectives and enhancing cross-cultural understanding. However, they were less motivated to use Facebook as the informal channel for socialization. The challenges encountered especially those concerning using Facebook in formal learning environments will be discussed. At the end, the recommendations for better utilizing and bringing together formal and informal online platforms will be suggested.