This paper presents the isolation of single crystals of an anionic Cu(II) complex (NH₄)(NHEt₃)[Cu₂(L)₄Cl₂]{HL = N-acetylanthranilic acid and NEt₃= triethylamine}. The analyses revealed the complex packing in the triclinic "P-1" space group in addition to its dimeric structure and the octahedral geometry around the Cu(II)ions. In the complex, all the four carboxylate ligands are bridging the two Cu(II) centers and the charge on the anionic complex is compensated by an ammonium and protonated triethylamine ions. This Cu(II) complex is interestingly exerting highly significant cytotoxic effect on MDA-MB-231 breast cancer cells with IC₅₀of 131.2 µg/ml and moderate anti-proliferative activity against both PC-3 prostatic cancer and T-24 transitional cell carcinoma cells with IC₅₀ of 200.7 and 300.3 µg/ml, respectively.