UV-Visible spectroscopy method has been developed for the analysis of Thiamine in biological and pharmaceutical product, based on a chromogenic derivatizing reaction using PDAB (P- dimethyl amino benzaldehyde) reagent. A Central Composite Design (CCD) design with response surface methodology was executed for optimization of experimental conditions of drug with a smaller number of experimental trials. Three independent factors, the concentration of PDAB, the volume of PDAB reagent, and volume of HCl, were used to construct a mathematical model and study the effects of these independent factors on responses as absorbance. The colored complex exhibits a Red shift with absorption maximum λmax at 425 nm, which was selected as the analytical wavelength. The drug seems to be linear, which was established via the regression analysis from 5-30 μgmL-1, with an R2 value of 0.998.The % RSD for intraday and interday precision was < 2%, with good recovery ranging from 95.02 to 101.43% with biological and pharmaceutical samples. LOD and LOQ of the developed method were found to be 1.51 μg mL-1 and 4.57 μg mL-1.This method can be used in routine analysis of pharmaceutical products containing aromatic primary amines along with an estimation of biological samples like urine, blood, sweat, faeces.