So far the students of Le Hong Phong Junior High School, Phan Rang City, Ninh Thuan province have been taught grammar with GTM (Grammar-Translation Method), which just prepares learners for conventional grammar-paper tests. Therefore, despite their considerable knowledge of grammar, the students fail to use the language they have learnt to communicate in real-life situations. Stimulated by this reality, the current study was carried out to investigate the effects of communicative grammar teaching on students’ achievement of knowledge of grammar and oral communication. The results of the current study have showed that after the treatment of communicative grammar teaching, the students’ achievement was proved to be significant in terms of knowledge of grammar and oral communication. In addition, communicative grammar teaching got positive attitudes from the students. Accordingly, the two major conclusions could be withdrawn from the findings that communicative grammar teaching was effective in (1) improving students’ knowledge of grammar and oral production, and (2) enhancing their interest in grammar lessons.