Abstract Three novel complexes of platinum(II) with R2edda bidentate ligands [PtCl2(R2edda)] (R=Me, Et, n-Pr; edda=ethylenediamine-N,N′-diacetate; 1–3), are synthesized and characterized by IR and NMR spectroscopy and elemental analysis. All complexes exist in three stereoisomeric forms (R,R), (S,S) and (R,S)(S,R). In addition crystal structure of one platinum(IV) complex [PtCl4((n-Pr)2edda)], 4, is presented. Furthermore, in order to assign stereoisomers of 1–3, a reduction of racemic [PtCl4(Et2edda)] by ascorbic acid to [PtCl2(Et2edda)] (2) was performed and analyzed by 1H NMR. Time-depending 1H NMR spectroscopic experiments were implemented to study the stability of ethylenediamine-N,N′-diacetate diesters. Finally, the in vitro cytotoxic activity of complexes 1–3 was studied on 11 tumor cell lines, 518A2 (melanoma), 8505C (human thyroid carcinoma), A253 (head and neck tumor), A431 (cervix), A549 (lung), A2780 (ovarian), MCF-7 (breast) and HT-29, HCT-8, DLD-1, SW1736 (all colon) by the SRB colorimetric assay method. Complex 3 showed the highest action against ovarian (A2780) cells with an IC50 value 51±1μM.