This study aimed to explore the effects of synchronous and asynchronous computer mediated communication (CMC) oral discussions on question types and strategies used by English as a Foreign Language (EFL) learners. The participants were randomly assigned to two treatment conditions/groups; the first group used synchronous CMC, while the second utilized asynchronous CMC. Students were asked to make six conversation sessions using CMC modes over six weeks. Students' conversations were transcribed and then analyzed per each discourse feature (question types and strategies) along with the CMC mode (synchronous and asynchronous). The findings of the study showed that students who used the asynchronous CMC mode produced significantly more discourse functions related to question types and strategies than students in the other treatment condition (synchronous group). It was also found that the asynchronous CMC mode encouraged learners to ask a series of questions which need long answers and seek more details through examples, clarification, and extension, while the synchronous CMC mode supports question types and strategies which are based on short answers that are clear and unambiguous. Highlights? Asynchronous CMC produced significantly more question types than synchronous CMC. ? Asynchronous CMC produced more question strategies than synchronous CMC. ? Asynchronous CMC supports questions with long answers. ? Asynchronous CMC promotes questions seeking more details. ? Synchronous CMC supports question which are based on short answers.