The present study investigated the effects of teaching lexical and grammatical collocation on Iraqi preparatory EFL learners’ writing skills. The design of the study was an experimental study. One hundred twenty males (N=120) Iraqi EFL learners took part in the present study. The setting was Babylon high schools. Quick placement test (QPT), writing test as pretest and posttest, and grammatical collocation, and lexical collocation as treatments were used as the instruments of the study. The participants in the experimental group were taught through collocation instructions. Moreover, two groups took writing test as pretest and posttest. In the experimental group, the researcher took part in the classroom as a participant and observe teachers' activities directly and teaching lexical and grammatical collocation were taught as treatment. All groups were taught by an EFL teacher. The researcher gathered information about what was happening in the classroom and he carefully observes the students during writing classes. The control group did not receive treatment. Based on results, teaching lexical and grammatical collocations had significant effects on the language learners’ writing ability. The results of the study can be useful for other researchers who are willing to study in this field, teachers and supervisors.
