This study investigated the effectiveness of Life Syllabus for decreasing aggressiveness of Iranian EFL students. The purpose of this study was to see whether there was any difference between Life Syllabus when a teacher used it in the classroom to reduce aggressiveness or not. A total of 206 Iranian EFL learners from four high schools in Bandar Abbas, Iran take part in this study. A quasi-experimental research approach with an interview followed in this study. A pre-test and post-test with the control and experimental group conducted to get participants’ performance before and at the end of using aggressiveness. The study lasted for one term with the naturalistic use of Life Syllabus for the experimental group. The comparison between the students’ scores showed that there was a significant difference in the final performance of two groups. Therefore, this study supports the idea that Life Syllabus reduces the EFL learners’ aggressiveness. As Life Syllabus proved to be useful with Iranian EFL learners, EFL teachers also can adopt the technique in their classes to advance their students’ language learning.