A simple, accurate, rapid and precise High performance liquid chromatographic (HPLC) method was validated for the determination of Assay of phenytoin sodium in phenytoin sodium capsules. The method employs Waters HPLC system on Inertsil ODS 3V, 250 x 4.6mm, 5μmcolumn with an isocratic elution at a flow rate of 1.0 mL/min using a mobile phase of 55-45% of Buffer and methanol. The detection was performed by a photo diode array and UVvisible Detector. In Linearity over concentration range of 50% to 150% correlation observed was 0.999. The intra and inter-day precision are with in limit (overall % RSD not more than 2.0 %). The overall mean recovery over a range 80,100, 120 % of phenytoin sodium was 100.8%. The method is robust even for slight change in chromatographic conditions. The validated method was Specific, Linear, Precise, Accurate, Rugged and Robust for Assay of phenytoin sodium in phenytoin sodium capsules. The method validated as per ICH guideline by High performance liquid chromatography.