Vocabulary learning and assessment are considered as the key basis for the training of English as a foreign language. However, it is time-consuming, uncertain and repetitious for the teachers to assess the proficiency of the students' vocabulary storage. This paper reports the results of a study which aimed to investigate the effect of Repeating as a direct vocabulary learning strategy versus Cooperating with Peers as an indirect vocabulary learning strategy teaching on the improvement of word knowledge on reading comprehension skill of Iranian undergraduate students. In order to attain the aim of the research, a vocabulary test was administrated to one hundred and forty-six male and female pre-intermediate EFL university students. Ultimately, seventy-eight pre-intermediate language learners were elected and appointed into two experimental groups (A and B) based on a vocabulary pre-test. The group (A) was taught vocabulary through Using Repeating vocabulary learning strategy and the group (B) was taught Cooperating with Peers vocabulary learning strategy for the aim of improving their lexical knowledge in reading comprehension skill. In the end of the treatment period, another vocabulary test (post-test) was implemented to all the students of two groups. After analyzing the data of the study that administered through using Independent samples t-test statistics, the results showed that there was a considerable difference between the two experimental groups under analysis in terms of their vocabulary improvements. The outcomes revealed that Repeating as a direct vocabulary learning strategy can cause to higher accomplishments of word storage in reading comprehension skill of Iranian pre-intermediate EFL undergraduate learners.