The present study investigates the knowledge of the speech act behavior of response to gratitude of Korean learners of English in comparisons with Korean native and English native speakers. While doing so, this study aims to reveal the cross-cultural differences between the two language groups. The data have been obtained from 43 Americans and 91 Koreans assigned to three groups: English native speakers; Korean learners of English; and Korean native speakers. Through a discourse completion test and a subsequent interview, the participants’ strategic usage of the speech act has been examined in terms of their perception of social factors and the choice of response strategies. The statistical procedure revealed little difference in the perception of the social factors between American and Korean participants. However, by different context and power relationship, they were found to use significantly different response strategies. Korean learners of English heavily depended on the earliest taught expressions in the classroom, such as “not at all” and “you’re welcome,” and used accepting expressions only infrequently. Korean EFL textbooks and classroom therefore need to include more diversified expressions in different contexts in which this English speech act occurs.