This study investigated what types of utterances Korean and Japanese high school students use when they express their gratitude which is one of the speech acts of greeting frequently used in their daily life. Also, it examined how honorifics and casual languages used for gratitude, considering honorific expressions are well developed in both countries. The conclusion to be drawn here can be briefly stated as follows. Speaking to the older, the same aged, and the younger people for conveying gratitude, high school students in both countries conducted direct speech(i.e. expressing the appreciation immediately and then keeping the conversation) prominently. In the situation that interlocutor is an intimate acquaintance, however, reason type speech(i.e. explaining the reason for the appreciation in advance, and then expressing thanks) and extra type speech(i.e. the type of speech except the others) were more observed than direct speech. Apology type speech(i.e. expressing thanks and apology at the same time) appeared more in Japanese students, on the other hand, reason type speech was often founded in Korean students. It is noticeable that the closer the relationship between the speakers was, the higher the rate of extra type speech was. In the speech of gratitude to the older people, a majority of high school students in Korea and Japan displayed honorifics. A few Japanese students did honorifics. In the case of the same aged people, it was characterized that all students from both countries exhibited causual language. With the younger people, the speech that the students used was various depending on the familiarity, social status, situations and speech context. It was more dominant in Japanese students and girl students than the counterparts of them.