A complete vibrational spectrum analysis of 4-hydroxyacetanilide is performed. The wavenumbers are calculated on the basis of density functional theory using B3LYP/6-31G* basis set.Vibrational analysis indicates that the lowering of stretching wavenumbers of methyl group due to electronic effects simultaneously caused by inducation and hyperconjugation is due to the presence of the oxygen atom. Comparison of the observed fundamental vibrational wavenumbers of 4-hydroxyacetanilide with calculated results is found in agreement with the experimental data. The predicted infrared intensities and force constants are reported.