The purpose of this study is to explore the influences of students' learning motivation on Web-based collaborative learning. This study conducted learning materials of Web pages about science and collaborative learning, a motivation questionnaire and interviews were used for data collection. Eighty Grade 5 students and a science teacher were recruited in this study. The controlled group involved 40 students who need to learn the dissolve concept on the Web pages, and complete the homework which was assigned by the Web pages by themselves. The experimental group involved the other 40 students and every four students were grouped in a team. The experimental group students not only need to learn the dissolve concept on Web pages, but also need to complete the homework which was assigned by the Web pages with team members. Besides, the experimental group students need to present their homework to other teams and provide feedbacks and suggestions to other teams. The results showed that experimental group significantly promoted their science learning motivation by using Web-based collaborative learning. (Contains 3 figures and 3 tables.)