The goal of this paper is to study meanings and functions of Korean qualifier ‘da’. ‘da’ is classifiedd into two categories; quantifying expressions and non-quantifiying expressions. There are some syntactic restrictions and semantic characteristics which distinguish adverb ‘da’ from noun ‘da’. Adverb ‘da’ usually modifies preceding elements in a sentence and is regarded to make them focus of the sentence. ‘da’ should be studied in semantic/pragmatic level in that ‘da’ fucntions as modal adverb. Especially, non-qualifying expression ‘da’ shows very peculiar semantic characteristics. Using non-qualifying ‘da’, speaker expresses unexpectedness and value judgment in their recogntion category. Moreover, ‘da’ indicates and modifies pragmatic situations. Sometimes it collocates with some modal propositions or is replaced by them. ‘da’ is used as modaliy expression in spoken language and discourse but it is not enough to define it as discourse marker.