Granted the fact that different cultures have different speaking styles, knowledge of these styles can help people grasp the essence of social cultural knowledge to communicate with others more successfully. In this regard, the present paper aims at comparing the use of speech act of gratitude in Persian and Chinese EFL learners and English native speakers performances to identify the existing pattern among them. For this purpose, the participants were asked to complete a Discourse Completion Task (DCT) designed by Eisenstein and Bodman (1993). The results revealed that although thanking is regarded as the most favorite strategy among all three groups, there are significant differences in the ways Persian and Chinese learners of English, and also native speakers of English use the speech act of thanking.