The present study investigates the effects of Task-Based Language Teaching on students' grammar knowledge in the field of teaching grammar. It has been studied with 32 students from 8th grade during a two-and-a-half-month process. Throughout this process, students firstly are applied a pre-test to examine their level and to confirm whether there is homogeneity between experimental and control groups. The findings on the pre-test results of the students do not yield meaningful results; and the study, especially the instruction process of grammatical structures launches. At the end of the instruction process, a post-test is applied to students to evaluate whether the progress between pre and post-test results are meaningful or not. TBLT raises significantly the grammar knowledge of the experimental students. Task-Based Language Teaching in teaching grammar yields meaningful results compared to traditional language teaching method in this study.