This study aimed to find out the effect of oral output and written output as two types of vocabulary instruction on Iranian EFL learners' listening comprehension and vocabulary learning. A pretest-posttest comparison group design, as one of the quasi-experimental research designs, was employed in this study. To this end, 40 male intermediate EFL learners within the age range of 14-18, studying at a Language Institute, participated in this study. At the beginning, pretests of vocabulary and listening comprehension were administered to determine the participants' initial listening comprehension ability and vocabulary knowledge and also collect a list of unknown words as the target words for the five treatment sessions. Each group practiced these words, one through the oral output instruction and the other through the written output instruction. Then, both groups took part in the posttests which were similar to the pretests. Within-group, results through Paired-Samples t-test showed that there were significant improvements in both the listening comprehension and vocabulary learning of the oral output group, while only vocabulary knowledge of the written output group was significantly improved from the pretest to the posttest. Between-group results through the Independent-Samples t-test indicated that oral output group significantly outperformed the written output group in the listening test, although no significant difference was found between their vocabulary test scores. The findings offer a wealth of opportunities to English teachers to employ the two types to enrich their instruction in order to motivate learners to expand their English vocabulary knowledge and become actively engaged in the listening process.