Although lexical competence is a part of communicative competence, it has not always been regarded as a priority in the field of language teaching and, therefore, it has failed to receive all the attention that it deserves. Moreover, the urgent need for training highly qualified specialists in language pedagogy places increasing demands on language teachers and their professional training. While a great amount of effort has concentrated on improving teachers’ language proficiency, little has been said and done on developing their skills in terms of professionally-oriented vocabulary. This article examines conceptual features of notions “lexical competence” and “professional lexical competence” concerning the process of training pre-service language teachers. The article also analyzes their actual definitions. Thus, a revised term “professional lexical competence of a language teacher” is introduced. Besides, the article depicts the content of lexical competence and its position within communicative competence of prospective language teachers. As a result of the analysis made, one can consider lexical competence and professional lexical competence regarding the process of training future language teachers as core, interdependent elements that contribute to the ongoing development of professional communicative competence and communicative competence respectively. Finally, steps for designing a training model for pre-service language teachers are enumerated.