In this paper, I tried to explain the function of Korean auxiliary verbs that appear together with a main verb within a sentence. From the viewpoint of grammaticalization, most of the auxiliary verbs exist at a middle point on the line of grammaticalization that starts from normal verbs. Therefore they tend to have some grammatical functions, without preserving their lexical meaning. That observation has led to a disagreement on the function of auxiliary verbs. The previous works have insisted that the auxiliary verbs are concerned mainly with ``aspectectuality``. We showed that Korean auxiliary verbs are divided into two subtypes of aspectuality, i.e. ``aspect`` and ``Aktionsart``, where the former is more grammaticalized than the latter. In addition, we also showed that the additional meaning that the verbs functioning as Aktionsart are assumed to have corresponds to ``modality``. As a result, some auxiliary verbs such as ``-e pelita``, ``-e nata``, ``-ko malta`` etc. have two meanings, Aktionsart and modality.