This study investigated whether English relative clauses play a significant role in textual cohesion, which is understood as textual connectivity and determination of sex and academic years in the perception and production of relative clauses of the Iranian EFL students. Therefore, 200 Iranian EFL language students (112 females and 88 males) majoring in English as a foreign language from Marvdasht and Shiraz Islamic Azad universities took two researcher-made tests, namely a reading comprehension test of 20 items and a writing test. Miltsakaki’s (2003) rules for pronoun resolution were utilized to score students’ answers. Semi-structured interviews were conducted with 30 English students to cross-validate the results of the tests conducted by the researchers. The results suggested that English relative clauses have an essential role in textual cohesion, which is understood as textual connectivity. The Kolmogorov-Smirnov Test and Mann-Whitney Test manifested that sex and academic year did not significantly affect Iranian EFL M.A. students’ understanding and production of relative clauses. The results of this study are of critical pedagogical implications for English as Foreign Language teachers, students, and course designers. Manuscript profile