Three novel complexes have been prepared through reactions of precursor [(dmso)2H][trans-RuCl4(dmso-S)2] (P) and 1,10-phenanthroline (phen) at different conditions. Whereas the analogs of mer-[RuCl3(dmso-S)(phen)] (1) and [Ru(phen)3]Cl2·6CH3OH (3·6CH3OH) have already been prepared by other synthetic routes before, product (H3O)[RuCl4(phen)]·4H2O (2·4H2O) is unprecedented. In the latter, isolated from highly acidic medium, one strongly bound dmso molecule in precursor P was substituted by chloride. Biological activity of 1 and previously isolated ruthenium-purine complexes ([mer-RuCl3(dmso-S)(acv)(CH3OH)] (4) (acv = acyclovir); [trans-RuCl4(dmso-S)(guaH)] (5) (guaH = protonated guanine)) was tested and compared. These data show that compounds 1, 4 and 5 are slightly cytotoxic against B-16 malignant melanoma cells but not against non-transformed V-79-379A cells. It seems that coordinated phen ligand increases the cytotoxicity of 1 in comparison to ruthenium precursor. The inability of tested compounds to induce lysis of bovine erythrocytes suggests that their cytotoxic effect is not due to the membrane damage.