Objectives: This study was conducted to explore the impact of IADL dependency on cognitive function decline in community-dwelling elderly. Methods: Data from the Survey of Living Condition of Elderly 3-year panel study were analyzed. The study subjects were 5,225 community-dwelling people aged 65 years or older who were normal in cognitive function at baseline. Use of medicines, management of finances, telephone use, and transportation were measured for IADL dependency. Logistic regression analysis was used to impact of IADL dependency on cognitive function decline. Results: Total IADL score(OR: 1.158, 95% CI: 1.050-1.277) and dependency of transportation(OR: 1.541, 95% CI: 1.097-2.165) were significantly associated with effect on the ADL decline of community dwelling elderlies adjusted for socioeconomic characteristics and baseline MMSE score. Conclusions: For early diagnosis of cognitive function decline, IADL should be monitored regularly. It should be emphasized that family, friend, and medical personnel of community dwelling elderly were aware of importance of IADL. Environmental modification for using transportation easily should be considered as a content of community health promotion program for elderly.