This study explores the integration of ChatGPT into a Business English writing class with 29 Taiwanese college students. The course covered 10 business correspondence genres, including resumes, cover letters, sales letters, inquiry and reply letters, complaint letters, and business reports. Students produced two drafts for each genre: one independently and one using ChatGPT. Two Business English experts—a teacher and an industry professional—evaluated the drafts. Students also reflected on their experiences through written feedback and post-course interviews, with qualitative data analyzed using thematic analysis. Results show that while ChatGPT effectively supported formulaic writing, such as sales and inquiry letters, it struggled with personalized genres like resumes and bios. However, the tool excelled in providing scaffolding, enhancing vocabulary, and improving grammatical accuracy and tone, often outperforming human-written drafts. These findings underscore the potential of generative AI in enhancing language accuracy and professional tone. This study argues for the adoption of AI tools in EFL classrooms to better prepare students for the evolving demands of global business communication.