In this study, solid lipid nanoparticle (SLN) suspensions were prepared using a base of hard fat with or without ethylcellulose (EC) and polyvinyl alcohols (PVA) and polysorbate (Tween) 60 surfactants. Commercially available PVAs vary in their degree of saponification and polymerization, and the appropriate PVAs to form SLNs from hard fat with or without EC were investigated. A relatively low-saponification-degree PVA was required to reproducibly form SLN suspensions without EC and relatively high-saponification-degree PVAs were suitable for SLNs with EC. The release of morin from SLNs with EC was more sustained than that from SLNs without EC. The maximum plasma concentration (Cmax) of SLNs with and without EC were almost the same, and both were higher than that of a morin suspension. The area under the curve for 0 to 360 min (AUC0-360) of SLNs with EC was increased compared with those of a morin suspension and SLNs without EC. The median diameter of SLNs with EC and a very low-saponification-degree PVA was decreased compared to other formulation, and morin release was more sustained for this formulation. SLNs with EC and a very low-saponification-degree PVA showed higher Cmax and AUC0-360 than SLNs with EC lacking a very low-saponification-degree PVA. The optimized SLNs with EC and a very low-saponification-degree PVA improved bioavailability via increased accessibility to the enterocyte surface by decreased particle size and increased permeation of SLN encapsulated morin through the intestinal membrane by sustained release properties.