This study investigates the differential effects of CMC interaction (both text-chat and voice-chat) and face-to-face interactions on university level of ESL students' vocabulary acquisition. More specifically, this study examines (a) whether learners engage in negotiated interaction when they encounter new lexical items, (b) whether CMC interaction help learners acquire new lexical items productively, (c) whether there are any special features related to negotiation routines in the most acquired words and the least acquired words, and (d) whether ESL students find CMC interaction helpful for their English learning. The participants consisted of 12 (6 male, 6 female) international students and visiting scholars at Iowa State University. The research design included a pre-test, a treatment activity, an immediate post-test, and a 1 week delayed post-test. The pre-test containing 24 vocabulary whose referents were auto parts items was given to choose the target lexical items. The type of treatment activity used in this study was an information-gap activity in which the students were required to request and obtain information from each other to complete the task. Two post-tests (immediate and delayed) were administered to assess the acquisition of new lexical items. The immediate and delayed post-tests were offered to students on the treatment day and 1 week after the initial treatment. Finally, a follow-up survey from each participant in CMC interaction group was also used to determine the strengths and weaknesses of computer-assisted language learning (CALL) task and the drawbacks or advantages of using such activities for language learning. The results showed that all ESL learners in both CMC and face-to-face interaction negotiated to complete their tasks, and all of the twelve target lexical items prompted negotiation for all of the dyads. Moreover, the results revealed that the students in all three groups recalled more than half of the previously unknown target lexical items in the immediate post-test and delayed post-test. For both productive oral and written acquisition, the results revealed that all three conditions seem to facilitate the acquisition of L2 words, as well as to ensure a good level of retention. However, there were no statistically significant differences between groups and posttests. Thus, meaning negotiation during computer-mediated and face-to-face interaction seems to promote both oral and written acquisition of L2 vocabulary. In addition, the results indicated that students tended to acquire new lexical items when they had some background knowledge about the target words or they were negotiating both form and meaning with their partners. A follow-up survey data showed that most of the students in both text-chat and voice-chat CMC interaction group had a positive attitude towards this type of activity in online, and they found synchronous chat as an interesting and helpful way of English learning.