In recent years, IELTS, an international English proficiency test, has been used as one of the criteria for admission into 103 university institutions in Vietnam (2023), which leads to an increasing demand to cram for the certificate among Vietnamese high-school students. However, the test presents a daunting task to the test takers as it requires both students’ language skills at an advanced level and general knowledge on a number of global issues. Among the four language skills tested, the writing component, particularly, the ‘task 2’ essay presents great challenges to test takers. This study aims to explore the difficulties that high-school students face when writing IELTS essays. A survey questionnaire was delivered to 60 students who are conducting an IELTS course at an English centre in Hanoi to identify and discuss their difficulties in writing IELTS essays. The study therefore hopes to provide some insights into their challenges in essay writing, as well as suggestions for teachers of English when accompanying with their students in preparation for the test.