Computer-mediated communication (CMC) has been used widely to engage learners in academic discourse for knowledge construction. Due to the features of the task environment, one of the main problems caused by the medium is information overload (IO). Yet the literature is unclear about the impact of IO on student learning. This study therefore investigated the influence of online students' perceived IO on their participation and knowledge construction in terms of cognitive and metacognitive processing as observed in online discussions via CMC. Interviews with students and computer conferencing transcripts were analyzed both qualitatively and quantitatively. The results indicated that students' perceived IO might influence their participation and levels of cognitive processing in online discussions. However, the results suggest that IO did not affect every student because some seemed to have learned how to manage IO. The results further suggest the critical role of learners' metacognitive competence regarding internal management of cognitive load.