Nanostructure-mediated drug delivery, a key technology for the realization of nanomedicine, has the potential to improve drug bioavailability, ameliorate release deviation of drug molecules and enable precision drug targeting. Due to their multifunctional properties, solid lipid nanoparticles (SLNs) have received great attention of scientists to find a solution to cancer. Vitamin supplements may contribute to a reduction in the risk of cancer. Vitamin B-12 has several characteristics that make it an attractive entity for cancer treatment and possible therapeutic applications. The aim of this study was to produce B-12-loaded SLNs (B-12-SLNs) and determine the cytotoxic effects of B-12-SLNs on H-Ras 5RP7 and NIH/3T3 control cell line. Results obtained by MTT assay, transmission electron and confocal microscopy showed that B-12-loaded SLNs are more effective than free vitamin B-12 on cancer cells. In addition, characterization studies indicate that while the average diameter of the B-12 was about 650 nm, B-12-SLNs were about 200 nm and the drug release efficiency of vit. B-12 by means of SLNs increased up to 3 h. These observations point to the fact that B-12-SLNs could be used as carrier systems due to the therapeutic effects on cancer.