Malnutrition substantially contributes to adverse clinical outcomes. However, no national survey has been conducted to characterize its epidemiology in hospital settings in China. We conducted the China Nutrition Fundamental Data 2020 project among a multistage stratified cluster sample of adult inpatients from 291 study sites across 30 provinces, autonomous regions and municipalities (except for Hong Kong, Macao, Taiwan Province, and the Xizang Autonomous Region, please see MATERIALS AND METHODS for details of the causes) of China to generate reliable data on the prevalence of malnutrition and explore the associated risk factors. We collected information on participants' sociodemographic characteristics, physical examinations, and laboratory test results. Malnutrition was defined according to the Global Leadership Initiative on Malnutrition (GLIM) criteria. The standardized prevalence of malnutrition was calculated, and factors associated with malnutrition were examined using logistic regression analyses. We included 54,652 individuals with seven systemic diseases who completed all the survey documents in the final analysis. The overall prevalence of malnutrition was 12.5%, representing 7.6 million adult inpatients in China. The prevalence of malnutrition was higher in men, individuals aged >= 60 years, residents of central and western regions, people from lower economic areas, and those with lower education levels than in women, individuals aged <60 years, residents of eastern regions, individuals from higher economic areas, and those with higher education levels. Patients with higher disease severity scores, infectious diseases, and neoplasms had a higher tendency for malnutrition than those without such conditions. Sex, age, region, economic level, education level, disease severity score, infectious diseases, and neoplasms were independently associated with malnutrition. In conclusion, malnutrition is prevalent among Chinese adult inpatients, necessitating national- and hospital-level interventions. This survey provides several avenues to begin addressing the burden of malnutrition in China.