Video captioning is a useful tool for vocabulary learning. In the literature, video captioning has been investigated by many studies, and the results indicated that video captioning is useful to foster vocabulary learning. However, most of the previous studies have investigated the effect of full captions on vocabulary learning. In addition, most of the previous studies have utilised the computer as a tool for the study. Very few studies have used mobile devices as a tool for the experiment. Therefore, this study aims at investigating the effect of keywords videos captioning on vocabulary acquisition using mobile devices. Thirty-four Arab EFL university learners participated in this study and were randomly assigned to two groups (keyword captioned video and full captioned video). The study is an experimental one in which pre- and post-tests were administered to both groups. The results indicated that keyword captioning is a useful mode to improve learner's pronunciation. However, there was no significant difference between the two modes of captioning.