Language is highly context-sensitive and contextual learning of grammatical rules shows how the rules can be used in sentences. In this line, the present study aimed to investigate the effect of diary writing on the correct use of English past tenses among Iranian pre-intermediate and upper-intermediate EFL learners. The study followed a quasi-experimental design with pre-test, treatment, and post-test, in control and experimental groups. To this end, a total number of 80 pre-intermediate and upper-intermediate learners were recruited based on convenience sampling and randomly assigned to the study groups. The results of two one-way ANCOVAs revealed that diary writing had a positive effect on the accurate use of English past tense at the pre-intermediate level but it did not show a significant effect among upper-intermediate learners. These findings can have efficient implications for EFL teachers, learners, syllabus designers, as well as material developers. EFL teachers can make use of diary writing as an effective method to help learners have a better grasp of English past tenses. Course designers and material developers are advised to have the results of this study under advisement and find a way to incorporate diary writing tasks in their curriculum to help learners get a better understanding of English tenses. Manuscript profile