Oxaliplatin with a low content of accompanying impurities originating from its preparation which contains, by weight, at most 0.01%, preferably less than 0.001%, of alkali metals, at most 0.0005%, preferably less than 0.0002%, of silver, and at most 0.01%, preferably less than 0.001%, of nitrates. A method for preparation of the said oxaliplatin resides in that a suspension of (SP-4-2)-dichloro-[(1R,2R)-1,2-cyclohexanediamine-N,N']platinum(II) in water is treated with silver nitrate, then, after removal of the solid phase, the obtained solution is treated with quaternary ammonium iodide of the formula (R).sub.4NI, the separated solid phase is removed and the obtained solution is treated with oxalic acid, and the separated oxaliplatin is isolated, washed with water and a polar organic solvent or their mixture, dried, recrystallised from water, washed with water and polar organic solvent or their mixture, and dried.