© 2016, Turkish Pharmacists Association. All rights reserved.A new high performance liquid chromatography method was developed and validated for the determination of quetiapine and its metabolites 7-hydroxy quetiapine and quetiapine sulfoxide in rat plasma. Separation was performed on a C18 column (Zorbax Eclipse Plus 4.6 mm ×100 mm, 3.5 μm particles) using a gradient elution at a flow rate of 1 mL/min. Mobile phase consisted of acetate buffer (10 mM, pH5) and acetonitrile. Analytes were detected with a DAD detector at 225 nm. Carbamazepine was used as internal standard in all analyses. Plasma samples were analyzed after a simple, one-step protein precipitation with acetonitrile. Separation time was 15 min including clean-up step. The method was validated in terms of precision, accuracy, recoveries, matrix effect and stability. It was found to be linearin the range of 0.065-130 μg/mL for quetiapine, 0.086-171 μg/mL for 7-hydroxy quetiapine and 0.042-83.35 μg/mL for quetiapine sulfoxide. All validation parameters were acceptable. This method was successfully applied to quantify the concentrations of the analytes in rat plasma.