Today English is the language widely used in the world. English is not only the national or official language of some countries, which have different cultures, but it is also the international language of communication in many fields including science, technology, business, entertainment and so on. Since Viet Nam joined World Trade Organization (WTO), the need for learning English has been considerably increasing among Vietnamese because their proficiency in English can help them get good jobs. Therefore, learning English is very necessary. However, it is not easy to master this language. In order to become good English learners, besides proficiency in listening, speaking, reading and writing skills, they must use grammar properly although English grammar can be difficult. Numerous studies show that the use of poor grammar in spoken and written statements reflects negatively on the speaker or author, and that people who use bad grammar are instantly perceived as being less intelligent, less reliable or less trustworthy than people who use proper grammar. Consequently, it is essential for English learners to master grammar. English grammar includes a lot of points. One of them is reported speech. Reported speech is important but rather difficult because it involves a lot of elements which causes students to feel confused and make many errors. Making so many errors of reported speech is not good because when someone reports incorrectly what someone else has said, it is difficult for listeners to understand or it is even easy for them to misunderstand, causing serious consequences. In addition, reported speech often appears on tests in class, final tests and tests in the entrance exams to universities and colleges. If students do not master this grammar point, they may lose marks relating to reported speech easily. For those reasons, the researcher decided to study the topic “Common Errors of Reported Speech Made by Grade 11 Students at Doc Binh Kieu High School, Tien Giang Province”.