5-(3,4,5-trimethoxybenzyl)pyrimidine-2,4-diamine (Trimethoprim) is used mainly in the treatment of urinary tract infections. Molecular mechanics studies of 5-(3,4,5-trimethoxybenzyl)pyrimidine-2,4-diamine (Trimethoprim) was performed according to the Hartree-Fock (HF) calculation method by Argus Lab 4.0.1 software. The molecular mechanics potential energy function were evaluated in terms of energies associated with bonded interactions (bond length, bond angle and dihedral angle) as well as non-bonded interactions (Vander Waals and electrostatic). Surfaces were created to visualize excited state properties such as highest occupied molecular orbital’s, lowest unoccupied molecular orbital’s and electrostatic potential (ESP) mapped density. The steric energy calculated for trimethoprim was 0.14364738 a.u. (90.14017290 kcal/mol), it Heat of Formation was estimated as 984.4882 kcal/mol and SCF energy was found to be -130.0072298778 au (-81580.8420 kcal/mol) as calculated by RHF/AM1 method at a net charge of 0 (zero) and valence electron of 94, as performed by ArgusLab 4.0.1 suite.These results could help us in understating the drug-receptor interactions.