This quantitative study examines the lexical features of IELTS Academic Writing Task 2 (IAWT2) essays written by Vietnamese non-English-major undergraduates, focusing on following writing prompts (WP): WP1 (encouraging bicycle use), WP2 (urban living and health), and WP3 (preferences for home-cooked versus fast food). A corpus of 479 essays was analyzed to explore the relationships between lexical density and content word types. Results reveal that nouns and adjectives significantly enhance lexical density, while verbs and adverbs contribute minimally. These results underscore the need for task-specific lexical training to improve students’ academic writing proficiency and vocabulary use in IAWT2.This quantitative study examines the lexical features of IELTS Academic Writing Task 2 (IAWT2) essays written by Vietnamese non-English-major undergraduates, focusing on following writing prompts (WP): WP1 (encouraging bicycle use), WP2 (urban living and health), and WP3 (preferences for home-cooked versus fast food). A corpus of 479 essays was analyzed to explore the relationships between lexical density and content word types. Results reveal that nouns and adjectives significantly enhance lexical density, while verbs and adverbs contribute minimally. These results underscore the need for task-specific lexical training to improve students’ academic writing proficiency and vocabulary use in IAWT2.