Abstract: In order to explore the isomeric effect on ¹⁴N nuclear quadrupole resonance (NQR) characteristics of nitrogenous compounds, the nicotinic and isonicotinic acids, serving as mutual isomers that both belong to carboxyl pyridines, were taken as research objects based on the NQR fundamental principles and hybrid orbital valence bond theories. In this paper, the similarities and differences of ¹⁴N NQR characteristics due to those of molecular structures were investigated from resonance spectra, characteristic parameters and hybrid effects. According to the comparative analysis about the experimental results, it can be found that there are plenty of similarities and differences in ¹⁴N NQR characteristics owing to the molecular isomerism. Or rather, in terms of resonance spectra, the similarities are reflected in spectral shape with differences in resonance point of the spectra for low frequencies. As far as characteristic parameters, the similarities are embodied in quadrupole coupling constant with differences in asymmetry parameter. With regard to hybrid effects, the similarities are concretized in hybrid form with differences in orbital occupation.