A reverse phase HPLC method has been developed and validated for the estimation of Aprepitant in Pharmaceutical dosage forms. An X-Terra RP -8, 150x4.6 mm, 5 μm particle size, with mobile phase consisting of Buffer (weigh and transfer 0.34g of Tetra-n butyl ammonium Sulphate in 1000ml of purified water, Add 1.1ml of concentrated Ortho phosphoric acid (88%) Mix properly) and Acetonitrile in the ratio of 50:50% v/v was used. The flow rate was 1.0 ml/min and the effluents were monitored at 210 nm. The retention time was 4.86 min. The detector response was linear in the concentration of 25-150 μg/ml. The respective linear regression equation being y = 22769x – 1489 (R² = 0.999). The limit of detection and limit of quantification was 0.28 and 0.84 μg/ml respectively. The percentage assay of Aprepitant capsules was found to be 100.02 %. The method was validated by determining its accuracy, precision and system suitability. The results of the study showed that the proposed RP-HPLC method is simple, rapid, precise and accurate, which is useful for the routine determination of Aprepitant in bulk drug and in its pharmaceutical dosage form.