Abstarct: Abstract: In this study, using the density functional theory, the properties of the drug molecule Ensitrelvir and its complex with some first-row transition mextal mextallofullerenes including chromium, iron, copper, and zinc were investigated as drug carriers. For this purpose, Gaussian and GaussView quantum software with the BLYP/LANL2DZ and then B3LYP/6-31G initial theoretical level were used to obtain the optimized structures of the compounds and to investigate the vibrational spectra of these molecules. In the thermodynamic properties analysis, drug adsorption on all mextallofullerenes is exothermic and with negative ΔG, and the iron drug-mextallocene complex is the most suitable complex thermodynamically. In the investigation of frontier orbitals, the energy gap is decreased in all complexes after formation, and the iron drug-mextallocene complex has the lowest ionization energy and electronegativity. Electrophilic attack points were identified by NBO and Fukui indices calculation. UV-Vis spectral data of the studied compounds were obtained at the B3LYP/6-31G theoretical level in the gas phase and without solvent. In the drug complexes with mextallofullerenes "C" _"19" Fe and "C" _"19" Cu, a redshift occurred, while in the complexes with "C" _"19" Cr and "C" _"19" Zn, a blueshift occurred. The iron mextallocene created a much longer wavelength and more stable complex after forming the complex with Ensitrelvir, and this difference in height and stability increase was also observed to a lesser extent for chromium, copper, and zinc mextallofullerenes.