Objective To evaluate the efficacy of anti-oxidative treatment in cats with pancreaticobiliary maljunction. Methods Thirteen healthy cats as control group were made a model that resembling the common channel of pancreaticobiliary maljunction as in humans，and were divided randomly into two groups：7 cats in untreated group were not treated，6 cats in anti-oxidative group were treated with melatonin，vitamin C， and vitamin E. Six months later， the gallbladders of these animals were removed and histopathological changes were evaluated by pathological and electron microscopic examination. The level of MDA，amylase concentration in the gallbladder bile，and percentage of proliferating cell nuclear antigen （PNCA） positive cells were also test. Results All cats had survived for 6 months after operation. The wall of gallbladder and the bile became thicker in untreated group than that in normal control group， and there were no significant differences between untreated group and anti-oxidative group. The gallbladder epithelium became villous in appearance in untreated group，although the epithelium of that in normal control group was flat with few folds. The epithelial cells of gallbladder arranged tightly in normal control group， while a significant change such as endoplasmic reticulum expanding， intercellular space broadening， and cellular nucleus deforming were observed in untreated group. The things in anti-oxidative group were better than untreated group. The amylase concentration in the gallbladder bile was （203.02±65.04）U in normal control group，（9 368.09±2 204.42） U in untreated group， and（8 746.25±2 077.95） U in anti-oxidative group， respectively. The amylase concentration in untreated group and anti-oxidative group were higher than that in normal control group （P=0.003），and there was no significant difference between the untreated group and anti-oxidative group （P=0.642）. The percentage of PNCA positive cells was （7.29±2.70）% in normal control group，（54.71±10.90）% in untreated group, and （48.17±13.06）% in anti-oxidative group， respectively （F=48.11，P=0.001），and the percentage of PNCA positive cells in untreated group was higher than that in anti-oxidative group （P=0.001）. The level of MDA was （1.095±0.653） nmol/mg prot in normal control group，（2.745±1.533） nmol/mg prot in untreated group, and （1.302±0.771） nmol/mg prot in anti-oxidative group， respectively （F=5.17，P=0.017）, and the level of MDA in untreated group was higher than that in anti-oxidative group （P=0.017）. Conclusion The anti-oxidative treatment is effective to pancreaticobiliary maljunction.