14 N NQR frequencies and T 1 's were measured between 54 and 150 K in crystalline trans -azobenzene which has two different molecular sites, orientationally ordered and disordered, at room temperature. The NQR parameters at 77 K were determined to be e 2 Q q / h =5.0150 MHz and η=0.4231 for the ordered site, and e 2 Q q / h =4.9619 MHz and η=0.4060 for the disordered site. The fine structure of each resonance line was observed by the Fourier transform method. It changes abruptly around 90 K, indicating the existence of a phase transition. The fine structures and their change at the phase transition can neither be attributed to the intramolecular dipole interaction between the two nitrogen nuclei, nor to crystallographic inequivalency of the molecules in the unit cell.