the purpose of the present study was to investigate the effect of task-based instruction of vocabulary on the receptive and oral productive acquisition of english vocabulary and compare the results with those obtained from the traditional method. the method and procedure applied in this study was as follows: after the implementation of opt, a group of sixty female students were chosen. the students were divided into two groups of thirty. one of the groups received a task-based method for the instruction of thirty english vocabulary items and the other one received instruction through a traditional method for teaching vocabulary. the thirty vocabulary items were instructed in three sessions. afterwards, the students took a meaning recognition test and an oral production test. two weeks later, similar tests were taken in order to measure the students’ long-term retention of the target words. the results revealed that there is no significant difference between the performance of the participants in the two groups in the immediate recognition and oral production tests of the target words. however, in the delayed recognition and oral production tests, a significant difference was found between the scores of the students in the two groups in favor of the task-based group.