Title: Utilizing an Inquiry-Based Instructional Model to Develop Preparatory School Pupils' EFL Writing Performance Author: Marwa Muhammad Ali Muhammad Supervisors: 1-Dr. Micheal  Abdel Maseeh   (Associate Professor of Curricula&  Instruction(TEFL), at Zagazig University,Faculty of Education) 2-Dr. Sahar El-Sayed El-Shura (Lecturer of Curricula Instruction (TEFL) Zagazig University,Faculty of Education) The results indicated that the experimental outperformed the control group that received regular instructions. The present study aimed at investigating the effect of utilizing An Inquiry-Based Instructional Model on improving EFL Preparatory Stage Students' Writing Performance. The research adopted the quasi-experimental design. The participants of the study were (fifty) second year preparatory School Students from Manshiat Naser preparatory school, Awlad Sakr, Al Sharqia Governorate, Egypt, who were equally divided into an experimental and control group. To achieve the purpose of the research, the researcher designed a writing performance questionnaire and a writing performance test. The material based on inquiry model was designed and taught to students at the second term of the academic year (2022-2023).