AbstractIt is shown that the phosphate‐methylated DNA miniduplex d(CpG)2 adopts a left‐handed Z‐type structure, whereas the phosphate‐methylated miniduplex d(GpC)2 is right‐handed. Furthermore, it is shown that elongation of the systems to the tetramer level results in right‐handed duplexes with rather low stability. The phosphate‐methylated hexamer d(CpGpCpGpCpG) is present in the single‐strand form. It is suggested that these results are of interest in the understanding of the exact role of salt cations in stabilizing the Z‐DNA structure of natural duplexes d(CpG…CpG)2 in high salt solution, since the methylated phosphate groups in fact mimic the situation of complete phosphate‐charge shielding. Therefore, it is concluded that exclusive cation‐phosphate complexation in the d(CpG)2 segments stabilizes the Z structure. 31P‐NMR experiments on the natural duplex d(CpGpCpGpCpG)2 at different concentrations of Mg2+ provided independent proof for the proposed model.