In acutely hospitalized older patients (≥65 years), the association between mild cognitive impairment (MCI) and malnutrition is poorly described. We hypothesized that (1) MCI is associated with nutritional status on admission and after discharge; (2) MCI is associated with a change in nutritional status; and (3) a potential association is partly explained by frailty, comorbidity, medication use, and age. We combined data from a randomized controlled trial (control group data) and a prospective cohort study (ClinicalTrials.gov: NCT01964482 and NCT03052192). Nutritional status was assessed on admission and follow-up using the Mini Nutritional Assessment—Short Form. MCI or intact cognition (noMCI) was classified by three cognitive performance tests at follow-up. Data on frailty, comorbidity, medication use, and age were drawn from patient journals. MCI (n = 42) compared to noMCI (n = 47) was associated with poorer nutritional status with an average difference of −1.29 points (CI: −2.30; −0.28) on admission and −1.64 points (CI: −2.57; −0.70) at 4-week follow-up. Only age influenced the estimates of −0.85 (CI: −1.86; 0.17) and −1.29 (CI: −2.25; −0.34), respectively. In acutely hospitalized older patients, there is an association between MCI and poorer nutritional status upon admission and four weeks after discharge. The association is partly explained by higher age.