Objectives: The aim of this study was to examine and compare the oral function of older people with mild cognitive impairment (MCI) or dementia. Methods: This cross-sectional observational study included participants with MCI or dementia aged 60 years or older. Global cognitive functioning was evaluated with the Mini Mental State Examination (MMSE) and the oral function was evaluated with subjective and objective assessments, including the perceived quality of chewing and swallowing, the function of the prostheses, the number of occluding pairs (OP), the degree of tooth wear and the active and passive maximum mouth opening. Results: The quality of chewing and swallowing was perceived as good in, respectively, 86.0% and 90.9% of the participants. Full or partial prostheses were worn by 63.8% of the participants, and the retention was good in 58.4% of the upper and 50.0% of the lower prostheses. Participants with MCI had a median of 3.0 (Inter Quartile Range [IQR] 0.0-7.5) occluding pairs, while participants with dementia had a median of 0.0 (IQR 0.0-1.0) occluding pairs, U = 3838.50, P < 0.001. There was a weak positive correlation between the number of occluding pairs and the MMSE score, r = 0.267, also when adjusted for age, r = 0.230. The median tooth wear score was 2.0 (IQR 2.0-2.0) in participants with MCI or dementia. The active maximum mouth opening was 45.8 (SD 9.3) mm in participants with dementia, while it was 49.8 (SD 8.1) mm in those with MCI, t(253) = 2.67, P = 0.008. Conclusion: For most participants with MCI or dementia, the swallowing ability and chewing ability were perceived as good. In addition, more than half of the prostheses had good retention and occlusion. Participants with more severe cognitive impairment had fewer occluding pairs and a smaller active mouth opening. The degree of tooth wear was less than one-third of the clinical crown in most participants with MCI or dementia.