A series of azoimine palladium(II) complexes of the general type cis-[PdCl2L] (1–6) {L = PhNNC(COMe)NC6H4X, where X = H (L1), CH3 (L2), Cl (L3), Br (L4), naphthyl (L5) and OMe (L6)} have been prepared by the reaction of cis-[PdCl2(NCPh)2] and the ligands (L) in acetone at room temperature. These complexes have been characterized by spectroscopic (IR-, UV–Vis and NMR) and electrochemical techniques. In addition, their biological activity has been studied via MTT test and by detecting the inhibition of clonal growth in three tumor cell lines, namely T47D human ductal breast carcinoma, MTLn3 murine mammary adenocarcinoma and RAW 264.7 murine leukemic monocyte macrophage. All of the tested palladium(II) complexes showed a noticeable antitumor activity. Complexes 4 and 5 showed a higher cytotoxic activity against human T47D breast tumor cell line than cisplatin, while comparable activity was observed against murine mammary MTLn3 adenocarcinoma cell line.