A new molecule having the structure of 6-methyl-3-phenethyl-3,4-dihydro-1H-quinazoline-2-thione (JSH18) was synthesized and it was possibly presupposed to show depigmentation through the inhibition of tyrosinase which is involved in the formation of melanin. Therefore, we are going to develop JSH18 as an inhibitor of melanin synthesis with topical formulations to show its optimal efficiency for skin whitening. Solid lipid nanoparticles (SLNs) play an important role as drug delivery systems for intravenous, peroral, parenteral, or ocular administration and for topical delivery. The particle size of prepared SLNs of JSH18 was variable from 59.8-919.6 nm. When the optimal SLNs cream (PU3) including 4 uM of JSH18 was applied to the backs of hairless rats for four days after the backs were irradiated by UV ray for seven days and the skin color was checked by reflectance spectrophotometer, the rat skin applied with PU3 cream quickly recovered to normal compared to SLNs cream without JSH18. Taken together, this study suggests topical formulations such as creams including SLNs with JSH18 might be an appropriate carrier for skin-whitening agents.