This paper examines the frequent occurrence of the word “nanka” in Japanese conversation through the perspective of “Interaction and Grammar” . This fi eld of research advocates that grammar is not static, but a resource that is used to achieve interaction. This paper mainly uses the method of conversation analysis to examine why at any given moment the speaker uses “nanka” , and what will be achieved by using the word. The results of the study are as follows. When the speaker faces an explanation of their previous words, they use nanka at the very beginning of the dialogue to express their “not clear of a specifi c reason” state. The speaker can use “nanka” in the absence of a suitable utterance to tell the hearer that they are searching for another word.