This work presents the synthesis and characterization of eight copper complexes [Cu(L-dipeptide)(neo)]·nH(2)O (neo = neocuproine) and their cytotoxic activities against tumor cell lines. The crystalline structure of [Cu(gly-val)(neo)]·3H(2)O, [Cu(gly-leu)(neo)]·H(2)O, [Cu(ala-gly)(neo)]·4H(2)O, [Cu(val-phe)(neo)]·4.5H(2)O and [Cu(phe-phe)(neo)]·3H(2)O were determined by single crystal X-ray diffraction. In all of them, the Cu(II) is pentacoordinated, in a square pyramidal environment. The coordination observed in solid state was retained in the major species in aqueous solution, as suggested by Electronic Paramagnet Resonance and UV-vis spectroscopies. The complexes were shown to have affinity for isolated DNA, as determined by Circular Dichroism experiments. Furthermore, biological experiments showed that all the complexes present high cytotoxic activity against the cell lines: MDA-MB-231, MCF-7 (human metastatic breast adenocarcinomas, the first triple negative), MCF-10A (human normal breast cells), A549 (human lung epithelial carcinoma) and MRC-5 (human lung epithelial cells). Together, these results suggest that these compounds are promising steps towards new effective drugs to treat cancer.