The training that instructors go through to get ready for teaching ESL/ESP is referred to as ESL/ESP instructors' preparation. Holliday, A. (2005) emphasized the significance of the linguistic theoretical background in instructors' preparation when he stated that instructors should advance their understanding of the linguistic theoretical background in order to understand how the teaching/learning process functions and to explain why it doesn't. Prospect ESL/ESP instructors who apply for work at Delta University for Science and Technology (Which has different faculties in multiples majors varying between Medical and Engineering majors) receive four weeks of academic instruction inside the faculty of Arts (English Language Department), followed by practical training, before starting their jobs in teaching undergraduate students in Medical and Engineering faculties. The purpose of the practical training is to provide these prospect ESL/ESP instructors the opportunity to put all the linguistics theoretical background they have learned into practice and evaluate the worth of the theoretical training. The primary goal of this study is to examine instructors' perceptions of the value of language proficiency both throughout their practical training and during their careers as ESL/ESP instructors. A descriptive-analytic research approach was used on fifteen ESL/ESP prospect instructors to achieve the study's goal. In addition to a framework of the course content, the prospect instructors were exposed to the period of the training.