A Gd(III) complex with tetrathiooxalate has been obtained by reacting trivalent lanthanide ion and tetraethylammonium tetrathiooxalate. Its synthesis and characterizations (EPR, ICP, FTIR, TGA) as well as its magnetic properties are reported here. The Gd(III)–Gd(III) magnetic interaction is weakly antiferromagnetic and the fit of the magnetic data leads to g=2.0 and J=−0.105 cm−1. A new Y(III) sulfate has also been obtained as a by-product during unsuccessful attempts of crystallization of an Y(III) complex with tetrathiooxalate. Its crystal structure has been determined and is described here. The chemical formula is Y(SO4)2.H2O.NH2(CH3)2 and it crystallizes in the space group P21/n with: a=8.5706(7) Å, b=19.6491(17) Å, c=5.6638(5) Å, β=90.522(1) and Z=4.