Purpose: To develop a sensitive and validated reverse phase-high performance liquid chromatographic (RP-HPLC) method for quantification of olanzapine in micro-sample of rat plasma using UV detection. Methods:A single oral dose of olanzapine (7 mg/kg) was given to overnight fasted rats (n = 6). Rat plasma samples containing the drug were extracted by liquid-liquid extraction using a combination of dichloromethane : n-hexane (80:20). A reverse phase chromatographic column C18 hypersil-BDS was used for chromatographic separation with a mobile phase consisting of 50 mM phosphate buffer pH 5.5, acetonitrile and methanol (50:30:20, v/v/v)