This study used UV spectrophotometry to determine the active pharmaceutical ingredient (API) in the dosage form from the AUC. Analyte concentration for AUC method, was measured using which combines absorbance over a predetermined wavelength range.This work describes the design, optimization, and validation of the AUC method, including selecting the appropriate wavelength range, generating the curve, and measuring stability and accuracy on track. The precision, accuracy and LOD & LOQ method for routine analysis in pharmaceutical laboratories have been demonstrated by verifying its performance according to International Committee for Harmonization (ICH) guideline. The AUC method provides a reliable and convenient method when measuring API in pharmaceutical forms using UV spectrophotometry. The Mobile phase used throughout the analysis of Cilnidipine is Methanol of HPLC Grade.