OBJECTIVE To develop the impurity control strategy of amoxicillin/potassium clavulanate. METHODS The impurity profiling changes of amoxicillin plus potassium clavulanate were compared with both amoxicillin and potassium clavulanate alone by HPLC. RESULTS Not only some new impurities were found. Both the impurities produced by amoxicillin or by potassium clavulanate in the complex medicine increased more quickly than in the antibiotics alone with acceleration test. CONCLUSION The results indicated that the impurity profiling of a complex medicine composed by b-lactam antibiotics and b-lactam inhibitor was not a simple mixture of both the components alone. The research should be focused on the interaction among the components influencing upon the impurity profiling of the complex medicine.