Abstract: All dimethylsulphoxide complexes of rare earth nitrates (except Pm) weresynthesized. Large dimensional crystals of La or Nd (60×28×25mm or 80×28×28mm respectively)were grown. The composition of complexes with fromLa to Gd is RE(NO₃)₃·4DMSO and those with from Tb to Lu (including Y)is RE(NO₃)₃·3DMSO. Because of steric hindrance causing by lanthanide con-traction, the number of the bound DMSO is decreased from 4 to 3 and thecoordination number is decreased from 10 to 9. Comparing the absorption spectra of Nd³⁺ ion in aqueous solution with those in DMSO solution,red shift of the spectral bands of Nd³⁺ ion in DM-SO solution has been observed, this implies that in the DMSO solution thereexists a certain degree of covalency in the RE-O bond. When the crystals are thermal decomposed in air at 850℃, the composi-tion of the thermal decomposed products of the trivalent rare earth ions beco-mes RE₂O₂SO₄(RE=Nd³⁺, Eu³⁺,Y³⁺). The magnetic susceptibilities X_g of all dimethylsulphoxide complexes ofrare earth nitrates have been determined. As the atomic number (Z) of rareearths increases they change periodically and there appear two maxima in theplot of X_gvs. Z. The absorption, excitation and fluorescence spectra of Pr (NO₃)₃·4DMSO and Tb(NO₃)₃3DMSO were determined.