In the previously reported C2O4(SnPh3)2 complex, the Sn(IV) centres are able to formally complete their coordination by addition of dimethyl sulfoxide (DMSO) molecules provided by the reaction medium, affording the title complex, C2O4(SnPh3.DMSO)2. The Sn(IV) centres are then pentacoordinated, with a common trans trigonal bipyramidal arrangement. The asymmetric unit contains one half molecule, which is completed by inversion in space group C2/c. The inversion centre is placed at the midpoint of the central bidentate oxalate dianion, C2O42-, which bridges the (SnPh3.DMSO)2 moieties. The molecule crystallizes as a disordered system, with two phenyl rings disordered by rotation about their Sn—C bonds, while the DMSO molecule is splitted over two positions due to a tetrahedral inversion at the S atom. All disordered parts were refined with occupancies fixed to 1/2.