Although corrective feedback (CF) has attracted much attention in the field of second language acquisition, there is scant research pertaining to CF in naturalistic written computer-mediated communication (CMC). This exploratory study addressed this gap by describing the types of CF that occurred and evaluating their relative effects on learner uptake in two conditions: (1) asynchronous CMC and (2) synchronous CMC between four Native Speaker-Non-Native Speaker dyads. As a measure of effectiveness, learner uptake is defined as immediate or delayed learner responses to CF. Participants completed the following synchronous tasks: an introductory task, and a video-prompted discussion task via an online chat program. For the asynchronous task, the participants co-developed a 3-day travel plan via email. The findings showed that CF in the form of clarification requests existed in the ACMC environment, whereas recasts were the only type of CF observed in the SCMC environment. Although no evidence of immediate effect was shown during task performance, an instance of delayed effect was shown across tasks in the SCMC environment.