This study investigates the impact of vocabulary knowledge on reading comprehension ability of Iranian English language learners receiving reciprocal teaching and cooperative grouping intervention program. To this aim, 80 students participated in the vocabulary test as the pre-test and they were asked to fill out the questionnaire. Then, they were distributed in four groups. Control groups (A & B) received the typical instruction of reading comprehension. On the other hand, experimental groups (A & B) received the intervention program. At the end of the course, all the students took part in the vocabulary test as the post-test and they were also asked to fill out the questionnaire provided for them after the post-test. The results were analyzed by the use of a series of independent –sample t-tests and MANOVA. It was found out there was relationship between vocabulary knowledge and the level of motivation in reading comprehension skill of Iranian EFL learner.

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