The present study attempted to investigate the effects of lexical bundles on Iranian EFL learners' paragraph writing production fluency. To achieve this purpose, an English language proficiency test was administered to 120 language learners studying TEFL at Islamic Azad University of Dehloran. Ultimately, 90 language learners were selected and randomly divided into two groups of control and experimental groups, based on their proficiency test scores. Both experimental and control groups worked on the same textbook content. The experimental group subjects were instructed on the lexical bundles use extracted from True to Life textbook, while the control group received placebo treatment during the course. The treatment took a whole academic semester. The results of the post-test showed that lexical bundles teaching methodology proved effective and influential in developing Iranian EFL language learners' paragraph writing fluency. So, developing English language skills, here writing skill in general and paragraph writing in particular, also, needs appropriate methods of which lexical bundles teaching methodology can be named. Since, lexical bundles use during instructional courses, help language learners have an automatic and easy recall of them in the process of paragraph writing, lexical bundles teaching methodology should be applied to having a better understanding of the textbook materials and to develop language skills. Therefore, the study suggests that content developers should include lexical bundles teaching methodology and their uses in the teaching and learning processes. The findings of this study gave empirical support to this view. Hence, this is pedagogically central in the domain of language teaching and learning and should be taken into account in the design and production of suitable instructional materials and in the methodology of classroom teaching and students learning behavior. To sum up, these findings can have a number of implications for material designers, language teachers, and students who are engaged in the teaching of English language as a foreign language.