An online visualization system of a discussion process in computer-supported collaborative learning (CSCL) has been developed to assist learners by enabling them to monitor the actual states of their discussion and allowing them to improve their learning community. The unique features of this system are 1) the learners have to select the most suitable category that represents his/her message content from the choices presented in the developed BBS and 2) the proposed system estimates the structure of the Markov from the stored categories? data sequences and visualizes the structure online. We demonstrate the effectiveness of this system using actual data and provide some evaluations. The results show that the proposed system motivates the learners and improves their methods of discussion.