Abstract: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has spread throughout the world, which becomes a global public health emergency. Undernourishment prolongs its convalescence and has an adverse effect on its prognosis, especially in diabetic patients. The purpose of this study was to evaluate the prevalence and characteristics of undernourishment and to determine how it is related to the prognostic outcomes in the diabetic patients with coronavirus disease 2019 (COVID-19). A retrospective, multicenter study was conducted in 85 diabetic COVID-19 patients from three hospitals in Hubei Province. All patients were assessed using the European Nutritional Risk Screening 2002 (NRS-2002) and other nutritional assessments when admitted. Of them, 35 (41.18%) were at risk of malnutrition (NRS score ≥3). Severe COVID-19 patients had a significantly lower level of serum albumin and prealbumin and higher NRS score than non-severe patients. Multivariate logistic regression analysis showed that serum prealbumin and NRS score increased the likelihood of progression into severe status (P<0.05). Meanwhile, single factor and multivariate analysis determined that grade of illness severity was an independent predictor for malnutrition. Furthermore, prealbumin and NRS score could well predict severe status for COVID-19 patients. The malnutrition group (NRS score ≥3) had more severe illness than the normal nutritional (NRS score <3) group (P<0.001), and had a longer length of in-hospital stay and higher mortality. Malnutrition is highly prevalent among COVID-19 patients with diabetes. It is associated with severely ill status and poor prognosis. Evaluation of nutritional status should be strengthened, especially the indicators of NRS-2002 and the level of serum prealbumin.