This study aimed at investigating the impact of Instructional Video Games (IVGs) on the vocabulary retention of Iranian language learners. To do so, 32 male and 43 female, between the ages thirteen to thirty one years old, in Padideh Derakhshan Institute, Sahinshahr, Isfahan, Iran were selected as a whole population. First, the World English placement test was administered, and 60 learners were chosen as the participants of the study. Next, a test of novelty as a pretest of vocabulary was administered at the early stage of the study to ensure the novelty of to-be-instructed words and participants' unfamiliarity with those words. The experimental group members were treated with the new way of learning, IVGs, to practice the new words in each lesson, but control group members were treated with by memorizing the new words through a list. After four weeks both groups sat for vocabulary posttest, and about one month later they sat for delayed posttest. The results were compared statistically. The statistical analysis indicated significant difference in vocabulary retention on learners of the experimental group.