Nowadays, English has been widely used in Vietnam.It is also a compulsory subject in many schools, colleges and universities. It is clear that people who want to master English should grasp its idiomatic expressions among other things. Obviously, to master a language, people cannot help studying idioms, one of the most valuable treasures of the language. In daily communication, we can see the frequent appearance of idioms. Anyone who much concerns idiomsowns a very attractive and academic manner of speaking. Inwritten texts, as well,writers use many idioms. Studying English idiomsin comparison withVietnamese ones, we can find the similaritiesand differences, which, therefore, help learners ofEnglish to understand and have a better use of English idiomsand Vietnamese ones. Being interested in idiomsfor a long time, I choose idiomsas mythesis topic. Due to the limited time and knowledge, I just focus on a very small part of the huge idiomatic treasure, ‘Idiomatic expressions containing the word ‘dog’ in English and Vietnamese’. With the aim of presenting an overview of idiomsin general and idiomatic expressions concerning the word ‘dog’ in English and Vietnamese in particular, I hope it will partly help learnersand translators avoid difficulties in realizing and translating English idioms into Vietnamese and vice versa.