The purpose of this study is to present the adverb-transformation of Korean adjectives, mainly used ‘adjective+key’ in the Basic Korean Dictionary. First, the comparative analysis with other adverbs(‘-i’ derivational adverb, adjectival root adverb of the same adjectival base) are done by observing the distribution in the corpus, so the statistical predominance and morphological fixation of ‘adjective+key’ which have overwhelming functional load is examined. Second the various semantic·syntactic characteristics of ‘adjective+key’ are analyzed such as the argument combination, movement, ellipsis, so the ‘adjective+key’ as morphological unit, not syntactic unit, is examined. Therefore we argue that ‘-key’ can be a kind of derivational affix and these ‘-key’ act as the adverb derivational affix like ‘-i’, which transform adjective into adverb when they combine with adjectives, ‘늘씬하다, 덩그렇다, 뻔질나다, 심심찮다’, in mainly used ‘adjective+key’ in the Basic Korean Dictionary.