This study investigated the effect of synchronous computer-mediated communication (CMC) text chat and voice chat on Iranian EFL learners' oral proficiency and anxiety. To this aim, 81 Iranian pre-intermediate EFL learners were selected from among 125 students at private English language institutes. The selected participants were divided into two experimental groups (synchronous text chat group and synchronous voice chat group) and a control group; each consisting of 27 pre-intermediate learners of English as a foreign language. Over a 6-week period, the participants in the experimental groups engaged in 60-75-minute-long chat sessions in dyads guided by a total of 10 tasks. The data were collected through pre-anxiety and post-anxiety scales and speaking tests. The analysis of the data revealed that both experimental groups had better performance on their post-test compared to their pretest scores, whereas there was a decrease in the anxiety levels only for the text chat group. The practical implications of the study and suggestions for further research are presented.