SLN with improved payloads and enhanced storage stability were investigated. Based on the experiences with solid lipid nanoparticles, a new type of solid lipid nanoparticle has been developed by incorporating triglyceride containing oils in the solid shell of the particle. The structure and mixing behaviour of these particles was characterised by DSC and (1)H-NMR. DSC yields information on the melting and crystallisation behaviour of the solid and liquid constituents of the particles. NMR is especially suited for the characterisation of the liquid oil domains inside the SLN. In this study a medium chain triglyceride oil was successfully incorporated in a matrix of a solid long chain glyceride (glyceryl behenate). The resulting particles were solid but the oil inside the particle remained in a liquid state. The relation between oil supplementation and melting point depression of glyceryl behenate proved to be linear. Mobility of the oil molecules inside the particles was considerably reduced compared to the emulsified oil. Moreover, two different chemical shifts for each of the lipid signals were observed indicating two different chemical environments. The experimental data is in line with a model describing uniform distribution of the oil molecules in the glyceryl behenate for low oil loads. However, at higher oil loads our data indicate the formation of oil clusters within the solid nanoparticle.