The present study aimed to determine the relationship between language learning strategies and vocabulary size in Iranian EFL learners. Therefore, 150 Zoha English Language Learners were given Oxford university and Cambridge university placement test. Oxford strategies inventory for language learning (SILL) were used, as well. According to Brown (2000) taxonomy, three classification of strategies as metacognitive, cognitive, social/affective strategies were included in the present study. Besides, Vocabulary Size Test based on the Norbert Schmitt's test, to measure the vocabulary size by assessing the learners' basic knowledge of common meaning of words in order to the relationship between language learning strategies and vocabulary size would be distinguished. After the data have been elicited, the results were statistically analyzed by using SPSS soft ware. The statistical study of the three proficiency levels manifest that the mean and standard deviation of metacognitive strategy is the most frequently used among others. It is also, understood that the employment of F-Test demonstrates that advanced proficiency level learners use the language learning strategies