Abstract: This study specifically intended to investigate the correlation between Farsi grammar knowledge and English grammar knowledge in relation to students' English language proficiency, age, gender, and linguistic intelligence. The study was conducted with 16 male and 19 female English literature undergraduate students studying at the Foreign Languages Department of state University of Qom, Iran. In this study, one questionnaire and three different tests were administered: a 20-item linguistic intelligence questionnaire in Likert scale model based on Gardner's Multiple Intelligence Theory, a 50-item Nelson Proficiency Test by which the participants were divided into two groups; „high‟ and „low‟ proficient, a 22-item multiple-choice test of Farsi grammar knowledge, and a 22-item multiple-choice test of English grammar knowledge. After scoring, some Pearson and Spearman Correlation Coefficient tests were run through SPSS software to investigate the relationship between Farsi and English grammar knowledge, and the relationships between grammar knowledge and English language proficiency, age, and linguistic intelligence. Also, an Independent-Samples T-Test was run to investigate sex differences in terms of L1/L2 grammar knowledge.