Molnupiravir (Mol) was the first oral antiviral drug which produced recently to provide an efficient benefit in lowering hospital admissions and fatalities from mild COVID-19. In the current novel, we introduce a new, rapid, simple, precise and selective spectrophotometric technique for the quantification of Mol antiviral drug in bulk and its pharmaceutical capsules. The spectrophotometric technique was based on the complexation of Mol drug with Fe(III) at pH =8 using borate buffer solution to create an intense blue complex. The complex displayed a maximum absorbance at 595 nm and followed Beer’s law within abroad concentration range of 1.0-130.0 µg mL 1 with high correlation value of 0.9998. Several experimental conditions influencing the stability and color intensity of the produced complex were examined and optimized. The molar ratio and Job’s continuous variation methods were developed to determine the stoichiometric ratio of the investigated complex, which was found to be 1:1 drug to metal ion. The Fe(III) solid complex is prepared and characterized using IR, UV-Vis., 1 H-NMR, 13 C- NMR spectroscopy. The Mol chelated as a bidentate ligand via NO atoms. The UV-visible spectra and magnetic moment analyses confirm the octahedral geometry with the smallest band gap. The present technique has high sensitivity and can be utilized for estimating Mol in two pharmaceutical capsules (Molnupiravir Eva Pharma and Molnupiravir Ramda). The results were compared to those produced by the previously published HPLC method and discovered to agree. Also, this study aimed to develop a rapid and accurate High Performance Liquid Chromatography (HPLC) method for quantification of Mol drug. The proposed HPLC method was validated and successfully applied for the quantification of Mol in molnupiravir capsules.