Artificial intelligence (AI) has emerged as a transformative force in higher education, reshaping the ways in which students acquire knowledge and develop language skills. Among recent AI-driven innovations, ChatGPT has attracted considerable attention for its ability to facilitate interactive, personalized, and context-sensitive language learning. Vocabulary knowledge, as a fundamental component of lexical competence, plays a central role in learners' communicative ability, reading comprehension, writing proficiency, and overall language development. Despite growing interest in AI-assisted language learning, empirical research examining the contribution of ChatGPT to vocabulary development remains limited, particularly within the context of higher education in developing countries. The present study investigates the potential of ChatGPT as an instructional tool for enhancing English lexical competence among university students. Specifically, the study explores how AI-assisted vocabulary learning supports vocabulary acquisition, contextual word usage, collocation development, lexical retention, and learner autonomy. Employing a quasi-experimental mixed-methods design, the research proposes comparing students who receive ChatGPT-supported vocabulary instruction with those who follow conventional vocabulary learning approaches. Data collection includes vocabulary achievement tests, learner perception questionnaires, classroom observations, and semi-structured interviews. Quantitative data are analyzed using descriptive and inferential statistics, while qualitative findings provide deeper insights into students' experiences and attitudes toward AI-assisted learning. The study is expected to contribute to the growing body of literature on artificial intelligence in language education by providing evidence of ChatGPT's pedagogical value in vocabulary instruction. Furthermore, the findings may assist educators, curriculum designers, and higher education institutions in integrating generative AI technologies into English language teaching in an effective, ethical, and learner-centered manner.