Abstract The m,;1n aim of the present study was to investigate the effect of task based language teaching on rdeveloping oral English performance pf Demot preparatory School grade ] ]students. To achieve this " objective, a task-based language teaching manual was prepared based on grade 11 English textbook speaking lessons, A quasi-experimental design was adopted and the sampling technique is purposive. An " oral performance test with an assessment rubric was administered. Two independent groups of Damot preparatory school were selected randomly as experimental and control group. One class (N=40) • representing the experimental group learned through the task-based language teaching while the other one class (N=40) representing the control group learned the same part following the traditional/regular teaching methodology. Data were collected from pre-test and post-test rated by two raters analyzed using • SPSS software using independent sample t-test and paired sample t-test. Results revealed that there were statistically significant differences between the mean scores of the experimental and control group subjects on H1eir oral English performance in favor of the experimental group after the treatment. Results also showed· statistically significant difference between mean scores of the experimental group' participants in the paired sample t-test of their pre-post test scores of oral English performance at . 05level. These results support that using task-based language teaching is effective on developing · students' oral performance. It was concluded that the task based language teaching has a positive effect on developing oral English performance of Damot preparatory school students. It is recommended that teaching speaking should be given more attention in our EFL classes, teachers should adopt TBLT, and more time Cd effort should be exerted to develop students' oral English performance. • .