To improve the dissolution rate of ibuprofen, a model poorly water soluble drug, self-nanoemulsifying drug delivery systems (SNEDDS) were developed. Various surfactants and oils were Screened as candidates for SNEDDS on the basis of droplet size of the resulting emulsions. The influence of the constituent structure, concentration and the composition of SNEDDS formulations, and the emulsifier HLB value, on the properties of the resulting emulsions was systematically investigated. Several SNEDDS formulations were employed to study the relationship between the emulsion droplet size and the dissolution rate of ibuprofen. The dissolution rate was accelerated by decreasing the nanoemulsion droplet size, and was significantly faster than that from a conventional tablet. The optimal SNEDDS formulation had a mean nanoemulsion droplet diameters of 58 nm in phosphate buffer, pH 6.8 (simulated intestinal fluid), and released ibuprofen more than 95% within 30 min. Therefore, these novel SNEDDS carriers appear to be useful for controlling the release rate of poorly water soluble drugs. (C) 2008 Elsevier Inc. All rights reserved.