Feedback(FB) has been defined as the 3rd move in the interactional exchange of the Initiation-Response-Follow up structure(Coulthard et al.,1975). In Japanese , it was also defined as a response or reaction to previous statements made by other participants (Takamor, 2004). On the basis of such definisions, the formula and function of FB has also been analyzed. On the other hand, Inter Relay Chat (IRC) is considred as a relativily "Lean" Medium as IRC, based on the data that comprises 5574 utterances taken from "Yahoo Japan" chat rooms. Qualitative analysis clarified that emoticons, the hedge in a form of the alphabet "w", and the verbal play and rhyme can be considred as the unique aspects of IRC in Japanese.