The purpose of this study is to investigate how learner variables, including language proficiency, motivation, effort, and family background affect Iranian language learners' EFL vocabulary strategy use? Subjects in this study were 450 EFL students (N = 450) at Payam e Noor University, Borazjan, Iran. After a placement test, they were grouped into different levels classes for teaching purposes and answered a vocabulary learning questionnaire during their regular English classes. After answering the questionnaire, collection was conducted by the author with the assistance of several English teachers and then underwent a series of statistical analyses by using the Statistical Packages for the Social Science (SPSS). Results of the study showed that the variable that had greatest effect on learners' vocabulary strategy use was motivation. Another important factor affecting vocabulary strategy use was family background, including family involvement, and years of study. Results of the study suggested that, teachers persuading of the students to adopt the most useful and effective vocabulary learning approaches will definitely have a positive effect on students' learning motivation and language performance.