It is known that thiosemicarbazide and its derivatives form stable coordination compounds with virtually all transition metals. Many of these compounds are biologically active, a property that allows their use as a base for selective microbiological culture media and makes them promising for applications as desinfectants and antiseptics. In many cases, the biological activity of drugs is correlated with their composition. Therefore, the synthesis and investigation of new biometal complexes with different ligands are of both scientific and practical interest. In this study we report on the crystal structure of bis{2-methyl-4[(methylcarbamothioyl)hydrazono](phenyl)methyl]-2-phenylpyrazolidin-3-ono}nichel dimethyl formamide solvate (I). The studied compound crystallizes in the monoclinic polar space group C2 (a=19.001(2), b=10.135(5), c=15.1635(1) Å, β=127.58(1)^o, V=2314.2(3) Å3). The Ni atom adopts the octahedral molecular geometry with distances of Ni-O, Ni-N, Ni-S equal to 2.036(4), 2.053(3) and 2.428(2) Ǻ, respectively (Fig. 1). Owing to the non-centrosymmetric space group of I, its nonlinear optical response was evaluated in solution by the electric-field-induced second harmonic generation method and in the solid state through the Kurtz-Perry technique.