Seven different dithiophosphonato Ni(II) complexes, [Ni(Xn)2], ((4-MeO-C6H4)PS2(OR)=Xn, R=3-pentyl-, X1; R=1-phenyl-1-propyl-, X2; R=4-tert-butyl benzyl-, X3; R= diphenylmethyl-, X4; R=4-tert-butyl cyclohexyl-, X5; R=3-phenyl-1-propyl-, X6; R=3-methyl-1-butyl-, X7) and three different dithiophosphinato Ni(II) complexes, [Ni(Yn)2], ((4-MeO-C6H4)PS2(R)=Yn, R=3-methyl-1-butyl-, Y1; R=2-methyl propyl-, Y2; R=1-methyl propyl-, Y3) were prepared by the reaction of NiCl2.6H2O and ammonium salts of the corresponding dithiophosphonic- and dithiophosphinic acids, [NH4][Xn] and [NH4][Yn], respectively. Starting with these complexes that were known previously new organo-dithiophosphonate salts of tris-phenanthroline Ni(II), [Ni(Phen)3][(Xn)2] and organo-dithiophosphinate salts of the same complex, [Ni(Phen)3][(Yn)2] were synthesized and characterized. Structural studies were based on spectroscopic methods (mass spectrometry (ESI), FT-IR, Raman spectroscopy), magnetic susceptibility measurements and elemental analysis. The crystal structures of [Ni(Phen)3][(X1)2], [Ni(Phen)3][(X3)2], [Ni(Phen)3][(X4)2], and [Ni(Phen)3][(Y2)2] were performed by single crystal X-ray diffraction analysis. All complexes were screened against human cell lines for assessing their cytotoxicity. Especially [Ni(Phen)3][(Y3)2]had the highest cytotoxic potency towards HepG2 cell line with IC50 value comparable to oxaliplatin. Moreover, [Ni(Phen)3][(X1)2]-[Ni(Phen)3][(X3)2] were found to be had significant cytotoxic activity in breast cancer cell line with the following IC50 values of 51.64 mM, 54.19 mM, 48.58 mM, respectively.