This paper investigates the most influential factor of anxiety in the English for Specific Purposes (ESP) context through classroom observation and questionnaires in a private vocational higher education in Indonesia. It also explores the differences in the anxiety level based on the year of study. One hundred seventy-one students participated in the study. The Foreign Language Anxiety Classroom Scale (FLACS) questionnaire was adapted to find out the students’ anxiety levels. The questionnaire was administered using Google form, then collected and statistically analyzed using SPSS. It was revealed that the most influential factor of students’ anxiety was the domain of Communication Apprehension. Furthermore, the ANOVA test showed that all students in each year suffered from anxiety. The most notable cause of the Communication Apprehension domain was performing without preparation. Self-negative evaluation was the primary cause of the Fear of Negative Evaluation domain. Meanwhile, for the domain of Test Anxiety, failure in language tests was the principal reason. This study implies that teachers should frame pleasant communication in the classroom as well as create fun and collaborative activities to reduce students’ anxiety.
