Recent studies have focused on the potential use of metal-based complexes for the treatment of cancer. However, there are some limitations of metal-based ligands for the treatment of cancer due to their toxic effects. In the present study, a novel bimetallic Cu(II) complex, [Cu-2(mu-(C6H5)(2)CHCOO)(3) (bipy)(2))](ClO4), has firstly been synthesized and characterized by FT-IR, and X-ray crystallography. Furthermore, Cu(II) complex-loaded solid lipid nanoparticles (SLNs) were initially prepared by hot homogenization method to overcome their toxic effects. After characterization, comparative cytotoxic and apoptotic activities of the complex and Cu(II) complex-SLNs on human breast cancer cells (MCF-7) and human umbilical vein endothelial cells (HUVEC) were determined. Cu(II) complex demonstrated considerable in vitro cytotoxic effects on MCF-7 (p<0.05) and induced apoptotic cell death (88.02 +/- 3.95%) of MCF-7 cells. But, the complex has also toxic effects (69.5%) on HUVEC control cells. For this purpose, Cu(II) complex-loaded solid lipid nanoparticles (SLN) were firstly produced, with a distrubution range of 190 +/- 1.45 nm to 350 +/- 1.72 nm and zeta potentials of -27.4 +/- 1.98 mV and -18.2 +/- 1.07 mV, respectively. The scanning electron microscopy (SEM) images of SLNs were also obtained. In vitro studies have shown that Cu(II) complex-SLNs help in reducing the side effect of Cu(II) complex (29.9%) on HUVEC control cells. Therefore, metal based complex might potentially be used for cancer treatment through nanoparticle based drug delivery systems.