The current research aims at developing EFL Majors' language performance in general, and writing in particular at Al-Azhar University in Palestine in the light of the inquiry approach. To achieve this, a group of 3 rd year, English department students (n=115) participated in the study. The researcher designed a writing performance test of 6 components; identifying main ideas, posing questions, paraphrasing, narrating, problemsolving and argumentation. The pretest revealed that most of the participants' writing performance was not up to the required level. Therefore, the researcher engaged them in a program based on the inquiry approach which took place in the academic year 2017-2018. This study employed the one group experimental design along with mixed research approach incorporating quantitative and qualitative analyses. After treatment, the post-test showed that there was a significant development in students' writing performance. Furthermore, the participants showed positive reflections towards the program. The study findings indicated the effect of the program in developing the participant's writing performance. In light of these findings, the researcher stated some pedagogical implications, limitations and recommendations.