OBJECTIVE: To investigate the effect of berberine on nuclear transcription factor kappaB (NF-kappaB p65) expression and translocation in insulin resistant 3T3-L1 adipocytes induced by free fatty acid (FFA) and its possible molecular mechanism. METHODS: 3T3-L1 adipocytes were treated with palmic acid (0.5 mmol/L) to induce insulin resistance and intervened with berberine. Controlled with aspirin, the glucose consumption in the medium was determined by glucose oxidase method; glucose transportation by 2-deoxy-[3H]-D-glucose method; protein expression of NF-kappaB p65 in adopocytes by Western blot; and the distribution of NF-kappaB p65 was displayed by confocal laser scanning microscope (CLSM). RESULTS: Treatment with 0.5 mmol/L of palmic acid for 24 h made glucose consumption of 3T3-L1 adipocytes decrease by 41%; the insulin-stimulated glucose transportation inhibited by 67%; nuclear NF-kappaB p65 protein expression and nuclear translocation of NF-kappaB p65 significantly increased. These changes were reversed by prior treatment with berberine or aspirin. But total NF-kappaB p65 protein expression was not responded to palmic acid, berberine and aspirin. CONCLUSION: Berberine significantly improve the insulin resistance induced by FFA in 3T3-L1 adipocytes, its molecular mechanism might through inhibiting the activation and translocation related gene expression of NF-kappaB.