The ^<35>Cl NQR absorption frequencies of 4,4'-dichlorodiphenyl sulfone have been measured as a function of temperature. This compound shows a single resonance line and a doublet, respectively, at room temperature and at 77 K, indicating the presence of at least two modifications. The phase change occurs near 152 K. The Zeeman effect of ^<35>Cl NQR line has been observed at room temperature in a single crystal. The quadrupole coupling constant and the asymmetry parameter are 68.592 and 0.098, respectively. There are two directions for the principal efg z axes making an angle of 100.4° which is coincident with the angle between the plane of the benzene ring. The single bond, ionic and double bond charactars are estimated, by means of the Dailey-Townes procedure, to be 0.718, 0.246 and 0.036, respectivly.