This action research study explores the integration of artificial intelligence (AI) tools into English for Specific Purposes (ESP) vocabulary instruction with the aim of improving both vocabulary knowledge and learning motivation among undergraduate Nutrition and Dietetics students at a private university in Türkiye. Recognizing the growing relevance of AI in education and the need for discipline-specific vocabulary in health sciences, the study adopted a mixed-methods design and was implemented over an eight-week period. During the intervention, students engaged in the creation of individualized vocabulary portfolios that incorporated weekly tasks supported by AI technologies, which were employed to assist students in defining ESP-specific terms, generating meaningful example sentences, producing relevant visual representations of vocabulary items, and reflecting on their learning processes. The instructional framework was guided by Nation’s Four Strands Model, which emphasizes a balanced focus on meaning-focused input, meaning-focused output, language-focused learning, and fluency development. Quantitative data were gathered through the administration of the Vocabulary Knowledge Scale (VKS) and the Vocabulary Learning Motivation Scale (VLMS) prior to and following the intervention. In addition, qualitative data were collected via an open-ended survey to better understand students’ perceptions, experiences, and attitudes toward the use of AI in their vocabulary learning journey. The findings indicate that the use of AI tools not only enhanced students’ ESP vocabulary acquisition but also positively influenced their motivation to engage in vocabulary learning tasks. These results suggest that AI-supported instruction can be an effective and engaging approach for vocabulary development in ESP contexts, particularly in health-related fields. The study provides practical insights for ESP instructors, instructional designers, and educational researchers seeking to implement innovative, technology-enhanced strategies in higher education settings.

Keywords: ESP vocabulary, artificial intelligence, vocabulary learning motivation, vocabulary portfolios.