The present invention relates to the area of platinum drugs. In particular, it relates to an improved process for preparing platinum complexes having the general formula (Ia) or (Ib): as defined of herein,comprising:1a) a first step, wherein [PtA4]2- is reacted with L under appropriate conditions in a first solvent to form [PtA3(L)]-；1b) a second step, wherein [PtA3(L)]- is reacted with L' under appropriate conditions in a second solvent to form cis-[PtA2(L')(L)]；1c) in the case where Y is halogen or hydroxy a third step, wherein cis-[PtA2(L')(L)] is reacted with H2O2, Y2 or halogen containing oxidant to form c,t,c-[PtA2Y2(L')(L)]； in the case where Y is carboxylate, carbamate or carbonate ester a fourth step, wherein an intermediate, where Y is hydroxy formed in step 1c), is functionalized with an appropriate acylating agent； and1d) in the case where A is not a halide or is different from the original halide, additional step(s) in which the original halide A of an intermediate formed in step 1a or 1b 1c or 1d is converted to a different halide or a new leaving group(s) A such as mono-dentate hydroxy, alkoxy, carboxylate or bi-dentate carboxylate, phosphonocarboxylate, diphosphonate, or sulphate.
