OBJECTIVES: Diabetes and prediabetes contribute to an increased risk of cognitive decline and dementia. Currently, it remains unclear whether elevated blood HbA1c levels, including prediabetes levels, affect reversion from mild cognitive impairment (MCI) to normal cognition. This study, therefore, aimed to examine the prospective associations of diabetes and prediabetes with reversion from MCI to normal cognition among community-dwelling older adults. DESIGN: Longitudinal cohort study with a 4-year follow-up. SETTING AND PARTICIPANTS: Community-dwelling older adults with MCI, aged ≥65 years at baseline (n = 787). METHODS: Participants' medical history of diabetes and blood HbA1c levels at baseline were assessed, and they were classified as control, prediabetes, and diabetes. Objective cognitive screening was performed using a multicomponent neurocognitive test at baseline and follow-up. Reversion from MCI to normal cognition over 4 years was determined. In the longitudinal analysis, we performed multiple imputations to adjust for a selection bias and loss of information. RESULTS: The reversion rates of MCI in the control, prediabetes, and diabetes groups were 63.4%, 55.6%, and 42.9%, respectively, in the completed follow-up dataset, and 54.6%, 47.2%, and 34.1%, respectively, in the imputed dataset. Multivariate logistic regression showed that diabetes decreases the probability of MCI reversion both before and after multiple imputations [odds ratio (OR) 0.37; 95% confidence interval (CI) 0.18-0.74 for before imputation, OR 0.37; 95% CI 0.19-0.72 for after imputation]. Furthermore, prediabetes also showed significantly decreased probabilities of MCI reversion both before and after multiple imputations (OR 0.57; 95% CI 0.34-0.94 for before imputation, OR 0.60; 95% CI 0.37-0.97 for after imputation). CONCLUSIONS AND IMPLICATIONS: Diabetes and prediabetes could inhibit MCI reversion. Adequate glycemic control may be effective in enhancing the reversion from MCI to normal cognition in a community setting.