The field of computer-assisted language learning has recently brought about a notable change in English as a Foreign Language (EFL) writing. Starting from October 2022, students across different academic fields have increasingly depended on ChatGPT-4 as a helpful resource for addressing particular challenges in EFL writing. This study aimed to investigate the use and acceptance of ChatGPT-4 in students' EFL writing. To this end, an experiment was conducted with 76 undergraduate students from a private school in Algeria. The participants were randomly allocated into two groups: experimental group (n = 37) and control group (n = 39). Additionally, a questionnaire was administered. The results showed that the experimental group (EG) outperformed the control group (CG). Besides, the findings revealed that students in the EG in post-test outperformed their pre-test scores. The findings also revealed substantial improvements in the EG's views of perceived usefulness, perceived ease of use, attitudes, and behavioral intention. According to the results, ChatGPT-4 helped boost students' EFL writing skills, which ultimately led to their acceptance. Students appear particularly interested in ChatGPT-4 because of its potential usefulness in putting what they learn about EFL writing into practice. Some suggestions and recommendations were provided.