A pharmaceutical composition includes an NAG-1 inhibitor as an active ingredient for inhibiting resistance against an anticancer drug of an ovarian cancer patient and a method of diagnosing prognosis of resistance against an anticancer drug of an ovarian cancer patient by using the NAG-1 inhibitor. It is found by controlling NAG-1 protein that NAG-1, which is overexpressed in an ovarian cancer patient and in an ovarian cancer stem cell having resistance against an anticancer drug, plays a key role in a chronic inflammatory reaction and resistance against an anticancer drug, and in this regard, NAG-1 can be used as a target gene for effective tumor therapy.