The aim of this study is to monitor, analyse and assess the effectiveness of using idioms in mastering students' vocabulary knowledge and improving speech in EFL class. The leading research method was a three-stage experiment. To successfully conduct the experiment, there were compiled a list of an active vocabulary and a list of English idioms that contain this vocabulary. All these were to meet the syllabus topics. A total of 62 school students were observed in this experiment. The obtained results were positive, indicating the fact that teaching vocabulary in idiomatic expressions turned out to be more appealing to learners and more effective than 'teaching laundry lists of vocabulary alone'. The paper discusses issues and practices of teaching topical vocabulary in EFL class and offers general recommendations for foreign language instructors.