This study investigates the use of a student's first language (L1) in teaching English for Specific Purposes (ESP) vocabulary to engineering students at a technical college in Ho Chi Minh City, Vietnam. It highlights a preference among teachers for using L1 while teaching, as well as the positive attitudes of students towards this approach, suggesting that L1 may facilitate comprehension and learning. The research provides insights into the extent of L1 usage and presents practical implications for improving ESP teaching methods in vocational training contexts.