Berberine is one of active alkaloids from Rhizomacoptidis in traditional Chinese medicine. The pharmacokineticsof berberine in rat plasma were compared betweennormal and chronic visceral hypersensitivity irritable bowelsyndrome rats (CVH-IBS) established by mechanical colonirritation using angioplasty balloons for 2 weeks after oraladministration of berberine hydrochloride (25 mg/kg) withthe equivalent dose of 22 mg/kg for berberine according tobody weight. Immunohistochemical analysis of c-fos andmyosin light chain kinase (MLCK) and immunofluorescenceanalysis of MLCK in rat colon were conducted. Quantificationof berberine in rat plasma was achieved by using a sensitiveand rapidUPLC-MS/MSmethod. Plasma samples werecollected at 15 different points in time and the pharmacokineticparameters were analyzed by WinNonlin software. Thegreat different pharmacokinetic behavior of berberine wasobserved between normal and CVH-IBS model rats. Compared with normal group, T1/2 and AUC(0–t) of berberinein the model group were significantly increased, respectively(573.21 ± 127.53 vs 948.22 ± 388.57 min; 8,657.19 ±1,562.54 vs 11,415.12 ± 1,670.72 min.ng/ml). Cl/F of berberinein the model group significantly decreased, respectively(13.89 ± 1.69 vs 9.19 ± 2.91 L/h/kg). Additionally,the expressions of c-fos and MLCK in model group werehigher than those in normal group. The pharmacokinetic behaviorof berberine was significantly altered in CVH-IBSpathological conditions, which indicated the dosage modificationof berberine hydrochloride in CVH-IBS were necessary. Especially, improved exposure to berberine in ratplasma inCVH-IBSmodel rats was attributed to increased theexpression of MLCK.