The new palladium (II) halide complexes with diethyl and dibutyl esters of (alpha-anilino-N-benzyl) phosphonic acid and diethyl and dibutyl esters of [alpha-(4-benzeneazoanilino)-N-benzyl] phosphonic acid have been prepared and studied. All organophosphorus ligands form dihalide complexes, trans-Pd(L)2X2(X = Cl or Br), with monodentate N-bonded ligand through the anilinobenzyl nitrogen in (alpha-anilino-N-benzyl) phosphonate complexes and through the azo nitrogen in [alpha-(4-benzeneazoanilino)-N-benzyl] phosphonate complexes, respectively, without participation of the phosphoryl group. Azobenzene containing ligands by ortho-metallation also form binuclear organo-palladium complexes, [Pd(L-H)Cl]2, with the metal-metal chloro bridge. The complexes have been identified and characterized by elemental analysis, infrared and 1H NMR, as well as by magnetic and conductometric measurements. All were tested in vitro for their cytostatic activity against KB and L1210 tumor cell lines. The results show that these complexes inhibit the multiplication of these tumor cells, but only the dichloro adduct of diethyl [alpha-(4-benzeneazoanilino)-N-benzyl] phosphonate was found to have activity comparable to that of the antitumor drug cisplatin.