Many studies emphasize the importance of preparing students with critical thinking skills, and these skills can be honed through classroom debate. During Covid-19 pandemic, however, it is impossible to carry out classroom debate. Therefore, this study focused on online debate through WhatsApp. Specifically, the present study aimed at finding out students' voices towards online debate through WhatsApp as alternative media to enhance critical thinking skills during Covid-19 pandemic. 17 undergraduate students participated in online debate for ten sessions throughout one whole semester. At the end of the research, 17 participants completed the survey questionnaires and 8 students volunteered to participate in semi-structured interviews. The results from both quantitative and qualitative data revealed that the participants found critical thinking skills important. Furthermore, the respondents believed that the online debate was good learning media to help them improve their critical thinking skills during this Covid-19 pandemic. The activity provided flexibility in terms of time and place. Other advantages, as claimed by the participants, included reducing students' anxiety, improving teamwork skills, and improving persuasion skills. However, some barriers were also found based on the participants' responses. The participants were concerned with the issue of being distracted, tendency to copy and paste, unstable network, and limited time.