As Vietnam is in a period of developing the country and broadening cooperation relations with foreigners, the role of English is getting more and more important. English has been used as an international language all over the world and as a means of communication with different purposes. For this reason, Vietnamese people want to acquire English for a variety of purposes. They study English to communicate with people from other countries where English is used as a native, second or just foreign language, to read English materials, or to pass the national secondary school exams. With such an important role, different aspects of the English language have been studied to gain different goals. In the area of cross-cultural communication, speech acts have been widely and carefully studied since they are highly culture-specific. They are conventionalised and governed by the rules of speaking characteristics of specific speech communities, therefore, interference or transfer may easily occur when speakers of different cultural backgrounds interact, which results in misunderstandings and communication breakdown (Suu, 1990).