Oral route is the most common route for the delivery of drugs because it is simple to implement and improves patient compliance.Nevertheless it is still face the challenge of oral absorption.The solubility, permeability biofilm and stability of drugs in gastrointestinal tract are important factors for oral bioavailability of drugs.As we all know, about 40% to 60% candidates or marketed drugs are water-insoluble (BCSII).It is the key that increasing solubility of BCSII drug in the gastrointestinal tract for their absorption.Lipid formulations, especially nanoemulsions have been recognized as an effective way to improve oral absorption of these drugs and have been caused great concern of researchers.The studies of our and other researcher have shown that BCSII drugs solubility can be increased significantly using the nanoemulsions and oral bioavailability of these drugs in vivo animal model also have been improved.However, in vitro cell model the absorption of thess drugs in nanoemulsions decreased significantly conversely with the increase of solubility in nanoemulsions.This means there are no relationships between in vitro and in vivo.The results also have indicated that mechanism of drug absorption in microemulsion cant be explained by Ficks first diffusion low (J=-D×dC/dx, Diffusion flux (J) is proportional to the concentration gradient at the unit of time and unit cross-sectional area).Further we have founded that the nanoemulsions will be breakdown in gastrointestinal tract by lipolysis and oral absorption of drugs in rats had a good IVIVC with dissolution increase by lipolisis of nanoemulsion.The oral absorption of drugs is affected by nanoemulsion formulation and physical and chemical properties of drug.