This study aimed to investigate the effect of teaching vocabulary through asynchronous social media on EFL learners' vocabulary learning and retention. To fulfill the objective of this study, the researcher selected 57 EFL learners through convenience sampling method. The participants were assigned randomly into two groups of the experimental (n=30) and the control group (n=27). The researcher made some posts based on the intended vocabularies (n=50). The treatment lasted for ten sessions. The researcher used Instagram for the participants of the experimental group. She posted five vocabularies for students of the experimental by use of Instagram. The participants of this group had to see the posts during two days and each one of them had to make a sentence with each vocabulary on comments section. The same vocabularies were taught to the participants of the control group through conventional method. The statistical results indicated that the participants of the experimental who used Instagram as a medium for instruction had significantly better scores in comparison to the participants of the control group in both posttest and delayed posttest. The outcome of the current study can be useful for language teachers, EFL learners and syllabus designers.