Nanostructured lipid carriers (NLC) made from mixtures of solid and spatially incompatible liquid lipids were prepared by melt-emulsification. Their drug loading capacity and releasing properties of progesterone were compared with those of solid lipid nanoparticles (SLN), and the NLC prepared by solvent diffusion method. Monostearin (MS) and stearic acid (SA) were used as solid lipid, whilst the oleic acid (OA) was used as liquid lipid. Properties of carriers such as the particle size and its distribution, drug loading, drug encapsulation efficiency and drug release behavior were investigated. As a result, the drug encapsulation efficiencies were improved by adding the liquid lipid into the solid lipid of nanoparticles. The drug release behavior could be adjusted by the addition of liquid lipid, and the NLC with higher OA content showed the faster rate of drug releasing. NLC had higher efficiency of encapsulation and slower rate of drug release than those of NLC prepared by solvent diffusion method. On the other hand, the NLC with higher drug loading was obtained, though the drug encapsulation efficiency was decreased slightly due to the increase of the amount of drug. The NLC modified with polyethylene glycol (PEG) was also prepared by using polyethylene glycol monostearate (PEG-SA). It was observed that the incorporation of PEG-SA reduced the drug encapsulation efficiency, but increased the rate of drug release. A sample with almost complete drug release in 24h was obtained by modifying with 1.30mol% PEG-SA. It indicated that the modified NLC was a potential drug delivery system for oral administration.