This case study aims at exploring international English as a foreign language (EFL) students' perceptions and employment of anonymity in online interactive learning. The study also investigates the impacts of the use of anonymity in EFL learning on students' learning performances. Participants of the study were 154 international EFL students enrolled in an Australian university, who came from different Asian countries. Multiple methods of data collection were administrated, including an online questionnaire with a five-point Likert Scale and open-ended questions, participants' reflective reports, and documents. Descriptive statistics were used to process the quantitative data. The qualitative evidence was categorized by themes and research questions. It was found that students' perceptions and employment of anonymity were different in two types of interaction. In peer interaction, participants were positive to anonymity and had active engagement in learning by using pseudonyms. In teacher-involved interaction, anonymity was less used, and was less influential on students' participation and production in EFL learning. It was also noted that participants exaggerated the positive effect of anonymity on their engagement in interaction. Recommendations for future studies are provided based on the findings.