The objective of the study is to discuss about the correlation between each group's performances of participation in online discussion and their achievements of project-based works. Performances of online discussion consist of content, frequency, and frequency of participation in discussion after each login into the Web community system. Research result reveals, in five groups, there are four groups with a positive correlation between their online discussion frequencies and their PBL works, however, there is a weaker correlation for one group of four. There is one group with a non-positive, even a negative, correlation between its online discussion frequency and its PBL works. All groups are with a positive correlation between their online discussion contents and their PBL works, however, there are weaker correlations for two groups. A fact is confirmed that backgrounds of members in three project-based groups would affect performances of their online discussion. Additionally, research result recommends the necessity of the establishment of the Jigsaw expert group discussion for learners involving project-based collaborative learning. However, there are some problems encountered during the process of Jigsaw method. Accordingly, the effectiveness of the expert group discussion is restrained. (Contains 4 tables and 3 figures.)