In this paper, I have accounted for some issues which are concerned with the Korean interjections. The findings are as follows. First, Korean interjection is a part of speech which is similar to sentences. Second, there are two criteria[e.g. functional criterion and structural criterion(the internal structure of interjections)] which can classify the Korean interjections on the perspective of word-formation. Third, based on the functional criterion, Korean interjections are classified into hesitative interjection, emotive interjection, reply interjection, call-up interjection, command interjection, and onomatopoeic interjection, etc. Fourth, based on the structural criterion(the internal structure of interjections), Korean interjections are classified into simple interjection(e.g. root interjection, base-modificated interjection, partial reduplicated interjection, etc.) and complex interjection(e.g. compound interjection, derivative interjection, full reduplicated interjection, ending-combined interjection, josa-combined interjection, etc.). Fifth, base modification is mostly involved in the formation of emotive interjection and onomatopoeic interjection. Sixth, nonmorphological word-creating rule and lexicalization are mostly involved in the formation of reply interjection, call-up interjection, command interjection.