The antitumorigenic potential of two palladium(II) complexes, [Pd(ca2-o-phen)Cl2] – C1 and [Pd(dmba)(dppp)Cl] – C2, was evaluated, using MDA-MB-435 cells, a human breast adenocarcinoma cell-line that does not express the estrogen receptor α (ER−). Growth inhibition and induced alterations in cell-morphology were analyzed. The sulforhodamine B test showed that, compared to control cells, both C1 and C2 significantly inhibited (p < 0.5) cell growth. The maximum effect with both was achieved with 1 μM complexes, after 24 h of treatment. No further cell-growth inhibition was achieved by increasing concentration or incubation time. Cell morphology was analyzed after staining with hematoxylin-eosin (HE). The morphological changes noted in the treated cells were cell rounding-up, shrinkage, nuclear condensation and reduction of cell length (p < 0.05), thereby indicating that both C1 and C2 are cytotoxic to breast adenocarcinoma cells. All together, there was every indication that, by decreasing cell growth and inducing morphological changes, the tested complexes are cytotoxic, hence their potentiality as promising candidates for antineoplastic drug development.