In Vietnam, after completing the high school education program, students who want to receive high school diploma, they must take a national examination including three compulsory subjects: Math, a foreign language, and Literature and electives in two groups: or Physics, Chemistry and Biology or History, Geography and Citizenship education. The method of exam-taking in the national examination greatly affected the teaching and learning style of teachers and students. In the process of teaching at high school, especially in the final year, the teachers studied how to ask types of question that have appeared in the national exam to focus on practising test-taking skills for students. Before 2017, the national examinations of Physics, Chemistry, Biology, Foreign Languages, Geography, History and Citizenship education consisted of all the multiple-choice questions; only in Math and Literature, essay questions were used. Since 2017, in national examinations of mathematics in Vietnam, there has been a significant change: the examinations with all essay questions with a time of 180 minutes (10 questions) were replaced by examinations with all multiple-choice questions (45 questions / 90 minutes). This change has met many conflicting opinions and has profoundly affected teachers' the method of teaching and reviewing knowledge and skills of mathematics for high school students in Vietnam. To better understand the perception of mathematics teachers - who directly teach - about this change, we conducted a survey of 50 mathematics teachers. The results showed that they were fully aware of the advantages of multiple-choice question-based examinations, and most of them wanted to maintain the use of multiple-choice questions for the following years.