Zeeman effect studies of ^<35>Cl NQR lines have been carried out at room temperature in a single crystal of 2,3,5,6-tetrachloronitrobenzene. It was revealed that the crystal belongs to a triclinic system and contains two chemically nonequivalent molecules in the unit cell. The angles between the C-Cl bonds and the angle between the aromatic rings were determined from the directions of the efg axes. The asymmetry parameters range from 10.7 to 12.4%. The bond characters of the C-Cl bonds were calculated from the experimental NQR parameters. The NQR lines were assigned by comparison with CNDO/2 and INDO calculations.