Objective To understand the comorbid conditions of physical illness in hospitalized elderly patients over 80 years old with mental disorders. Methods The study screened inpatients from Beijing Anding Hospital affiliated to Capital Medical University from January 1， 2010 to December 30， 2017. Patients with diagnosis based on ICD-10， age of ＞ 80 years old， and complete clinical files were selected. The comorbid conditions of physical illness and other information in the selected patients were investigated. Results Among the 187 patients， 183 patients had physical illness， with a comorbid rate of 97.9% and an average of 6.9 comorbidities. There was no significant difference in the number of comorbid physical diseases among patients with different mental disorders（ P ＞ 0.05）. In terms of the average number of comorbidities， mental disorders and mood disorders caused by brain damage and dysfunction， and other physical diseases had significantly fewer comorbidities than other four types of mental disorders（ P＜0.05）. A total of 183 elderly psychiatric patients had a total of 1 297 cases of physical illness. There are 769 cases of diseases in the nervous system， circulatory system， endocrine system， respiratory system and digestive system， accounting for 59.29% of all cases of physical illness. The top five diseases were hypertension（ 115 cases， 62.8%）， constipation （84 cases， 45.9%）， cerebral infarction（ 71 cases， 38.8%）， diabetes（ 54 cases， 29.5%）， and coronary heart disease（ 48 cases， 26.2%）. The number of comorbidities of physical illness in patients is related to age（ P＜0.01）Conclusions The physical comorbidity of elderly patients over 80 years old with mental disorders is very common. The number of comorbidities is large， with cardiovascular and metabolic diseases accounting for the majority.