Maslinic acid (MA) is a natural pentacyclic triterpenoid with inherent antitumor activity which has a very low solubility in water. MA solid lipid nanoparticles (SLNs) were prepared using Poloxamer 407 and Dicarboxylic acid-Poloxamer 407 as surfactants. Both MA SLNs are monodisperse, with sizes around 130 nm, and stable. Curcumin has been encapsulated in both types of nanoparticles without altering their colloidal properties. Moreover, SLNs greatly improve the solubility of MA and Curcumin. The cytotoxicity of MA and SLNs has been evaluated in BxPC3 human pancreatic cancer cells, MCF7 human breast cancer cells, and in a human fibroblast primary cell line. MA shows higher cytotoxic effect in BxPC3 and MCF7 cancer cells than in human primary fibroblasts. Nile Red loaded MA SLNs are quickly uptaken by BxPC3 and MCF7 cells, and show different cytoplasmic distributions depending on the cellular line. The oral or intravenous administration of MA SLNs in mice does not report any toxic effect, and the intravenous administration of fluorescent MA SLNs shows a homogeneous distribution in mice, without site-specific accumulation. Results suggest the great potential of MA SLNs as nanocarriers of anticancer drugs and as promising targeted theranostic nanodevices.