The ground state conformation, vibrational frequencies, and ¹H- and ¹³C-NMR chemical shifts of acetylsalicylic acid (aspirin, ASA) were calculated by using ab initio Hartree-Fock (HF) method and density functional theory (DFT) (B3LYP) with 6-311++G(d,p) basis set level. After determining the ground state conformation of the molecule, the needed calculations were done. The calculated vibrational frequencies, optimized geometric parameters (bond lengths and bond angles) and chemical shifts were found to be well in agreement with the corresponding experimental data. The comparison of the observed and calculated results also showed that the scaled DFT(B3LYP) method is superior to the scaled HF method for all the calculated data.