The faculty of mixed copper (II) compound with optically active forms of serine (Ser) and butyrin (But) Cu(D-Ser)(D-But) to crystallize in polytypic modifications was traced on the basis of obtained crystallographic structure data by electron diffraction technique. The unit cell parameters, the space groups of symmetry and the numbers of formula units per unit cell of two obtained polytypic modifications are: I - a=10.17(2) Å, b=9.60(1) Å, c=5.07(1) Å, γ=92.3(2)0, P21, Z=2; II - a=20.35(2)Å, b=9.59(1) Å, c=5.08(1) Å, γ=92.3(2)0, C21, Z=4;