The aim of this work was to develop and validate the assay test for Tetrabenazine in the pharmaceutical dosage forms by HPLC. The assay method by HPLC was found to be linear in the concentration range of 20 to 100 μg/mL. The mobile phase was composed of acetonitrile and buffer pH: 6.8 potassium dihydrogen phosphate (60:40 v/v) the flow rate of 1 mL/min using UV detection at 215 nm. The results of the analysis were validated by recovery studies. The percentage recovery method was found to be 99.33-100.87%. The LOD and LOQ were found to 0.04 μg/mL and 0.15 μg/mL. All the parameters of validation were in the acceptable range. This developed method was successfully applied to estimate the amount of Tetrabenazine in the tablets.