Carmustine and lomustine nitrosoureas disintegrate to produce reactive intermediates that serve as classic alkylating agents in the body. Carmustine is given intravenously, while lomustine is administered orally. They both act as anti-cancer drugs; both could be used to treat brain tumors. To know the correct synthesis and reactivity of the molecules, structural analysis is very important. This research indicates the characterization of carmustine and lomustine drugs by quantum chemical measurements. The aforementioned compounds were optimized and the bandgap energies were calculated using DFT and HF methods at various basis sets. For all calculations, the B3LYP/6-311++G level has been chosen. For the two molecules, some parameters such as bond length, bond angle, and dihedral angle were calculated. Also, HOMO – LUMO energies were calculated to predict the more reactive molecule; the calculations included ionization potential, electron affinity, electronegativity, dipole moment properties, chemical hardness, and chemical softness. Moreover, electrostatic molecular potentials and Mulliken atomic charges were also described. All calculation results showed that lomustine is more reactive compared to carmustine.