AIM: Previous studies have reported significant associations between tooth loss or periodontal status and cognitive function; however, animal experimental studies have shown that occlusion might be a more important factor in cognitive decline. The purpose of the present study was to investigate the influence of a lack of posterior occlusal support by residual teeth on the decline of cognitive function over a 3-year period among 80-year-old Japanese people. METHODS: Participants were community-dwelling older adults (n = 515, age 79-81 years). Cognitive function was measured using the Japanese version of the Montreal Cognitive Assessment. At baseline, participants were divided into two groups: those with and without posterior occlusal support. Participants whose Japanese version of the Montreal Cognitive Assessment score decreased by ≥3 points over the 3-year period were defined as the declined group. Logistic regression was carried out for the decline in Japanese version of the Montreal Cognitive Assessment scores, including dental status and possible risk factors as independent variables. RESULTS: More participants without posterior occlusal support tended to be in the cognitive decline group (49.4%) than in the maintained group (38.5%; χ2 -test, P = 0.02). Logistic regression analysis showed that a lack of posterior occlusal support was a significant variable (odds ratio 1.55, P = 0.03) for cognitive decline, even after adjusting for other risk factors. However, the number of teeth or mean periodontal pocket depth was not significantly correlated with cognitive decline. CONCLUSIONS: The present findings suggest that a lack of posterior occlusal support predicted the incidence of cognitive decline, even after adjusting for possible risk factors in community-dwelling old-old people. Geriatr Gerontol Int 2018; 18: 1439-1446.