For many years we are carrying out the synthesis and investigations of the atomic structure, crystallochemistry and biological activity of binary and mixed compounds of metals with αamino acids in order to create the new materials with useful properties on the basis of coordination compounds. This investigations were initiated and made under the leadership of Academician Anton Ablov. We have obtained the copper(II) complexes with different acid residues, serine (Ser) and threonine (Tre) in solid state. These compounds possess the biological activity, in particular – antitumor activity. The atomic structure and crystallochemistry of three modifications of the mixed complexes of the composition CuSerTre, containing optically active antipode of serine and threonine in the proportion D:L=1:1 in these composition were studied by electron diffraction technique. According to obtained data, the elementary structural unity of these modifications are the mixed complexes Cu(D-Ser)(L-Tre) and Cu(L-Ser)(D-Tre). The complexes are associated in the separated layers in the structure and the complexes are concentrated in the separate one-dimensional structural units (rows) in the layers. It was determined, that the layers of the mentioned modifications are built only from the same initial one-dimensional structural units (rows) and differ one from another only by the way of their neighboring in the layers limits. In such a way, the layers are two- dimensional polytypic structure. In the layers the polytypic structure is formed by the reflection of onedimensional structural units in the plane and turning around the two-fold screw axes. Besides that, the layers are also arranged in different mode one to another in the structure. In two modifications the layers are tied together by translation [100], and in the third one by translation [½ ½ 0]. In this case the predominant role in the realization of the polytypism is played by the interaction of methyl and hydroxyl groups of the serine and threonine residues of the adjacent layers.