Manganese (Mn)-based complexes have been drawing attention due to the fact that they are more effective than other metal complexes. However, the use of Mn(II)-based complexes in medicine remains limited because of certain side effects. The aim of this study was to investigate the cytotoxic and apoptotic effects of a novel Mn(II) complex [Mn-2(mu-(C6H5)(2)CHCOO)(2)(bipy)(4)](bipy)(ClO4)(2) and Mn(II) complex loaded solid lipid nanoparticles (SLNs) on MCF-7 and HUVEC control cells. The average diameter of Mn(II) complex was about 1120 +/- 2.43nm, while the average particle size of Mn(II) complex-SLNs was approximate to 340 +/- 2.27nm. The cytotoxic effects of Mn(II) complex and Mn(II)-SLNs were 86.8 and 66.4%, respectively (p<.05). Additionally, both Mn(II) complex (39.25%) and Mn(II)-SLNs (38.05%) induced apoptosis and increased the arrest of G(0)/G(1) phase. However, Mn(II) complex exerted toxic effects on the HUVEC control cell (63.4%), whereas no toxic effects was observed when treated with Mn(II)-SLNs at 150M. As a consequence, SLNs might be potentially used for metal-based complexes in the treatment of cancer due to reducing size and toxic effects of metal-based complexes.