S-Alkylisothiosemicarbazones form an important class of thiosemicarbazone derivatives. Much attention has been paid to the synthesis, structure and biological properties of coordination compounds with these ligands.     The aim of this work is the synthesis, study of structure and antitumor activity of two nickel coordination compounds with methyl N'-[(2-hydroxynaphthalen-1-l)methylidene]-N-(prop-2-en-1yl)carbamohydrazonothioate (L1) and ethyl N'-(2-hydroxybenzylidene)-N-(prop-2-en-1yl)carbamohydrazonothioate (L2). The coordination compound I was synthesized by the reaction between ethanolic solutions of nickel(II) perchlorate and L1 in 1:2 molar ratio. For the synthesis of the complex II it was used the same molar ratio, taking ethanolic solutions of nickel(II) acetate and L2·HI.     The X-ray diffraction analysis has been used for structural characterization of studied compounds. Complexes I and II exhibit octahedral environment of  nickel atoms (Fig. 1 a, b). The compound of I was found  to crystallize in non-centrosymmetric space group P212121. In the crystal the perchlorate molecule links the complexes by hydrogen bonds (Fig. 1a). The crystal of II has the centrosymmetric space group C2/m and this complex forms the H-bonds only with iodine atom in outer coordination sphere (Fig. 1b). The synthesized compounds selectively inhibit the human promyelocytic leukemia HL-60 cells growth in the range of concentration 10-5-10-7 mol/L.