The reaction of cis-[PtCl₂(Me₂SO)₂] with 1 equiv. of each of the amidoximes RC(NH₂)NOH in neutral media in MeOH results in the formation of complexes cis-[PtCl₂{RC(NH₂)NOH}(Me₂SO)] (5 examples; 83-98% isolated yields). In the presence of 2 equiv. of NaOH in MeOH solution, the reaction of cis-[PtCl₂(Me₂SO)₂] with 1 equiv. of each of the amidoximes RC(NH₂)NOH leads to [Pt{RC(NH)NO}(Me₂SO)₂] (7 examples; 74-95% isolated yields). All new complexes were characterized by C, H, and N elemental analyses, HRESI⁺-MS, IR, ¹H, ¹³C{¹H}, and CP-MAS TOSS ¹³C{¹H} NMR spectroscopies, and additionally by single-crystal XRD (for seven species). The cytotoxic potency of six compounds was determined in the human cancer cell lines CH1/PA-1, A549, SK-BR-3, and SW480. Generally, the second class of complexes containing chelating amidoximato ligands shows much higher cytotoxicity than the non-chelate amidoxime analogs, despite the lack of easily exchangeable chlorido ligands. Especially, the complex [Pt(p-CF₃C₆H₄C(NH)NO)(Me₂SO)₂] displays a remarkable activity in the inherently cisplatin resistant SW480 cell line (0.51 μM vs. 3.3 μM).