The present study offers some insight into the effect of vocabulary strategy training on developing vocabulary size and overall language proficiency. It also explores the correlation between vocabulary strategy use and the language development learners achieve. A total of 52 third-year English majors were selected from the Faculty of Languages and Translation, Misr University for Science and Technology as participants of the study. Three instruments were required to fulfill the purpose of the study; English proficiency test, vocabulary learning strategy inventory and vocabulary size test. ASSURE model based program was designed to cater for training participants on vocabulary learning strategies. Findings indicated that the experimental group students outperformed the control group in both vocabulary size and overall language proficiency. Positive correlation was also found between learners' language performance and their strategy use. It is recommended that conscious vocabulary learning strategies should be accorded attention in EFL preparation programs with prominence given to autonomy- fostering lexical learning activities.