Amidst the rising importance of English as a Lingua Franca, this study is conducted with the aims of investigating EFL students' perceptions and practices regarding the use of ChatGPT for developing English argumentative essay writing skills, thereby bridging the gap in understanding the role of AI technologies in enhancing language learning outcomes. The study focused on eight (8) aspects for developing writing skills, including (1) Vocabulary, (2) Grammar, (3) Idea generation, (4) Organization, (5) Translation, (6) Writing style, (7) Plagiarism management, (8) Mechanics of writing, for which EFL students use ChatGPT to improve their English argumentative essay writing skills during the course Reading-Writing B2.2. A ninety-two-item questionnaire was administered to investigate the perceptions and practices of using ChatGPT to develop English argumentative essay writing skills. The study sample consists of 100 students who have taken the Reading-Writing B2.2 course. The findings revealed that students had a positive attitude toward the use of ChatGPT for their enhancement of writing argumentative English essays. They found a negative correlation between the extent of perception impacts on students’ practices, meaning that when students’ perception of using ChatGPT increases, their engagement tends to reduce. Moreover, the result showed that while practices vary significantly across groups, perceptions remain relatively consistent among students. The insights from this study stand to significantly advance our understanding of the role of AI tools like ChatGPT in enhancing English argumentative essay writing skills among EFL students. By uncovering students' perceptions and practices regarding the use of ChatGPT, this research offers valuable insights for educators. With a deeper understanding of student attitudes and behaviors, teachers can tailor their teaching approaches to better support learners, fostering more effective language learning environments.