Objective: To characterize the clinic features of fulminant type 1 diabetes mellitus(FT1DM). Methods: It was a retrospective study analyzing the clinical and laboratory data of patients diagnosed as FT1DM and type 1 diabetes in the Department of Endocrinology in China-Japan Friendship Hospital from January 2011 to November 2015. Results: A total of 125 newly diagnosed type 1 diabetic patients were included in the study, 14 of them (11.2%) met with the criteria of FT1DM. The age at onset was (35.8±8.3) years. The time from onset to ketosis was 2(0-7) days. The plasma glucose levels were extremely high[ (33.79±14.13)mmol/L], while glycosylated hemoglobin A1c[HbA1c, (6.9±0.7) %]and serum glycosylated albumin [(21.8±4.5)%] levels were only slightly above the normal range. Moreover, the C-peptide levels were extremely low and the situation kept after one month to two years' follow-up. Four (28%) patients were glutamic acid decarboxylase antibody (GADA) positive at the onset with two turned negative. One patient was GADA negative at the onset and turned positive after one month. The levels of serum transaminases increased with enlargement of liver in one of the patients after insulin therapy, who was diagnosed as glycogenic hepatopathy. Conclusions: FT1DM is an extremely rapidly progressing type of diabetes and life threatening disease. Causations have to be taken in medical practice.