Very poor oral health, common among older adults, is associated with cognitive decline.This study aimed to investigate the association between denture use, chewing ability, and cognitive function in Korean middle-aged adults using samples representing middle-aged people at the national level. This longitudinal study included 9,998 middle-aged adults via Korea Longitudinal Study of Aging 7th special survey data. Denture use, chewing ability, health-related factors, and general characteristics were assessed by the Computer Assisted Personal Interview. After controlling general characteristics using a generalized estimating equation model, the association of denture use and MMSE scores with chewing ability of those with or without dentures and MMSE scores were analysed. Twenty-four percent of participants wore dentures among them, 35.1% complained of difficulty chewing when wearing dentures. Among participants who did not wear dentures, 16.4% complained of difficulty chewing. MMSE scores were lower among denture-wearers than non-denture wearers (β = -0.026, p < 0.001). In both groups, MMSE scores decreased with chewing difficulty and were significantly reduced among non-denture wearers (p < 0.05). Chewing ability was closely associated with cognitive function. Given the negative effect of difficulty chewing on cognitive function, maintaining chewing ability should be of great concern.