This study aims to strategically use computer-mediated communication (CMC) tools to build online communication environments for problem-based learning (PBL). A six-stage process was proposed for online PBL learning in this study: 1) identifying the problem, 2) brainstorming, 3) collecting and analyzing information, 4) synthesizing information, 5) co-building knowledge, and 6) refining the outcomes. The one hundred undergraduate students who participated in this study were randomly grouped into 13 groups. Multiple methods of data collection were adopted to investigate students' learning activities in the online PBL course. The methods of data triangulation and investigator triangulation were used to analyze the following: 1) the use of CMC tools, 2) students' learning achievement, 3) students' experience in the online PBL course, and 4) group learning activities. The empirical evidence showed that students were able to communicate, discuss, and co-build the knowledge from the collected information. With the online communication, they were able to seek solutions to the problems in learning activities. Meanwhile, students were satisfied with the online PBL course. The successful experience of course design in this study can encourage instructors to use open-source or free-hosted CMC services to develop online PBL courses. (Contains 1 table and 4 figures.)