Abstarct: In this research, the strnght of intramolecular hydrogen bonding of (4-salicylideneimino) benzo-15-crown-5 (4SEB15-C-5) was investigated by means of density functional theory (DFT) calculations, quantum theory of atoms in molecules (QTAIM) and the natural bond orbital (NBO) analysis. 4SEB15-C-5 optimized at the B3LYP/6-311++G** level of theory then the results of molecular structure, vibrational frequencies, the chemical shifts of 1HNMR and the topology of in bond critical point of N···H were compared with the analogous parameters of N-salicylidenaniline (SAN). From geometrical parameters, the main effect of 5-crown-5 ether substitution on nitrogen of aniline ring in 4SEB15-C-5 is slightly shortening of the N···H distance and lengthening of the O–H bond length in comparison with the corresponding values for SAN. The Hـb of proton of OH bond in 4SEB15-C-5 is downfield by 0.96 ppm from SAN. From AIM results for these compounds, the range of −VC/GC ratios are between 1, 2 and the values of HBCP are negative in critical point of N···H bond, so the interaction of N···H bond for these compounds is partially covalent in nature. Also, the laplacian of electron density, and the total energy density, HBCP, in critical points of N···H bond of 4SEB15-C-5, SAN have positive and negative values, respectively, so these compounds are classified as the systems with medium hydrogen bond. Comparison of the molecular structure, vibrational spectra and AIM results of 4SEB15-C-5 with those of SAN reveal the following trend in the hydrogen bond strength: 4SEB15-C-5 > SAN.