Objective To analyze the clinical features of latent autoimmune diabetes in adults (LADA) and adult- onset type 1 diabetes mellitus (T1DM) of different durations, and investigate their differences in order to found theoretic basis for rational diagnosis and treatment of LADA. Methods Clinical data of all hospitalized patients with LADA and those with adult- onset T1DM admitted in Peking Union Medical College Hospital from Jan. 2007 to Dec. 2014 were collected and analyzed retrospectively. The clinical characteristics and complications of the two diseases were explored with the duration of disease. Insulin dosages and oral administration of drugs were compared between the 2 groups of patients for the therapeutic features of LADA. Results There were 78 patients with LADA and 110 patients with adult- onset T1DM recruited in this study. Compared with the patients with adult- onset T1DM, those of LADA had older age of onset (P<0.01), larger body mass (P<0.05), lower incidence of diabetic ketoacidosis (P<0.01), decreased serum level of HbA1c (P<0.05), and higher positive rates of glutamic acid decarboxylase antibodies (GADA) and insulin antibodies (IAA) (P<0.05). For the patients with the disease duration of ≤5 years, LADA patients had higher level of fasting C peptide but lower level of HbA1c, and lower dosage of insulin when compared with adult- onset T1DM patients. The islet function was decreased obviously with the duration of disease in the both groups. But no significant difference was seen in the incidences of complications between the groups. There were more LADA patients treated in the combination of insulin and oral hypoglycemic drugs (mainly α- glucosidase inhibitors). Conclusion Compared with adult- onset T1DM patients, the LADA patients are older at the age of onset, heavier of body mass, of unobvious tendency of ketoacidosis, and higher positive rates of GADA and IAA. Though the clinical features of LADA are similar to those of T2DM at the onset (with gradually decreased islet β cell function), the features become consistent with those of T1DM with its progression (with almost loss of the function). In the treatment of LADA, oral hypoglycemic drugs should be combined to keep blood glucose stable.