Abstract: Objective：To compare the clinical characteristics of early-onset type 2 diabetes mellitus (T2DM) patients with different body mass index (BMI). Methods：Totally 287 cases of initial-diagnosed T2DM patients (age≤35 years old) were divided into overweight group (BMI≥24 kg/m2, n=190) and normal-weight group (BMI＜24 kg/m2, n=97). The general information and biochemical indexes were compared between the two groups. Results：Compared with the normal-weight group, the overweight group had significantly higher proportion of male patients, significantly higher prevalence of hypertension and non-alcoholic fatty liver disease (NAFLD, P<0.01). Compared with normal-weight group, the patients in overweight group had significantly higher levels of fasting glucose (FPG), fasting serum insulin (FINS), postprandial 2-hour insulin (2 h INS), fasting C-peptide (FC-P), postprandial 2-hour C-peptide (2 h C-P), insulin resistance index (HOMA-IR), alanine aminotransferase (ALT), aspartate aminotransferase (AST), γ-glutamyl transpeptidase (γ-GT), total cholesterol (TC), triglyceride (TG), serum creatinine (SCr), and uric acid (UA, P<0.01). While the levels of glycated hemoglobin (HbA1c), glycated albumin (GA), high density lipoprotein cholesterol (HDL-C) were significantly lower than those in the normal-weight group (P<0.05). Conclusions：Early-onset and overweight T2DM patients have a higher prevalence of hypertension and NAFLD, with more serious liver and renal dysfunction, HOMA-IR, and metabolism disorders.