This study aims at examining of the function and necessity of marking of register in Korean Dictionary focusing on middle-scale dictionary, and how to mark the register label into headwords in objective ways. Register can be specified to honorific, humbleness, argot, slang, vulgar, and spoken. The register label is the very useful information for users, compilers, scholars of dictionary. It is very important to mark the register label. In spite of the importance, it is a fact that the standards dividing the register label and metalanguage are vague. However, we presented to classify these according to the objective standards shown up in the speech situation and use.