Abstract: To prevent the inflammation in the anterior chamber,topical antibiotic and corticosteriods(such as dexamethasone、cefuroxime etc)are often used after the surgery.A method combining liquid chromatography (LC) with tandem mass spectrometry(MS/MS)was developed to quantify dexmethasone in aqueous humor and plasma.Before narrow-bore LC/MS/MS analysis,aqueous humor was performed by liquid -liquid extraction,and plasma was extracted by solid-phase extraction.Prednisone was used as an internal standard.The standard curve was composed of six points ranging from 1.08 to 54μg/l(averageγ 2=0.9995).Limits of detection was 0.4μg/l Imprecision was <5% across the therapeutic range.Dexmethasone recovery averaged over 77% With its high sensitivity and specificity,this LC/MS/MS method presents a valuable tool for metabolism studies.