The study reported in this article investigated the pragmatic failure of Iranian EFL students in expressing gratitude when interacting in English. A discourse completion test (a written questionnaire) was given to 60 native speakers of English in London and 60 Iranian senior students of English repressing two proficiency groups. Participants were asked to respond in writing by indicating what they would say if they were in similar situations of the questionnaire. The results clearly indicated that Iranian EFL learners used expressions of gratitude which resembled those of the Iranians speaking in Farsi, and differed from those of the native speakers of English. Furthermore, it was found that the difference between the two proficiency groups was not statistically significant in the majority of the situations.
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