Context: Berberine is an active alkaloid isolated from Rhizoma coptidis [Coptis chinensis Franch. (Ranunculaceae)] that is widely used for the treatment of diabetes, hyperlipidemia and hypertension. However, the pharmacokinetics of berberine in normal rats and type 2 diabetes mellitus (T2DM) model rats are not clear. Objective: This study compares the pharmacokinetics of berberine between normal and T2DM model rats. Materials and methods: The T2DM model rats were fed with high fat diet for 4 weeks, induced by low-dose (30mg/kg) streptozotocin for 72 h and validated by determining the peripheral blood glucose level. Rats were orally treated with berberine at a dose of 20 mg/kg and then berberine concentration in rat plasma was determined by employing a sensitive and rapid LC-MS/MS method. Results: The significantly different pharmacokinetic behaviour of berberine was observed between normal and T2DM model rats. When compared with the normal group, C-max, t(1/2) and AUC((0-t)) of berberine were significantly increased in the model group (17.35 +/- 3.24 vs 34.41 +/- 4.25 mu g/L; 3.95 +/- 1.27 vs 9.29 +/- 2.75 h; 151.21 +/- 23.96 vs 283.81 +/- 53.92 mu g/h/L, respectively). In addition, oral clearance of berberine was significantly decreased in the model group (134.73 +/- 32.15 vs 62.55 +/- 16.34 L/h/kg). Discussion and conclusion: In T2DM model rats, the pharmacokinetic behaviour of berberine was significantly altered, which indicated that berberine dosage should be modified in T2DM patients.