Micro/sub-micron emulsion and related systems have received a lot of attention in the last years for their common use as vehicles for topical administration. These systems can be defined as fine emulsion dispersion with droplet sizes in the sub-micron range. The main advantages of such systems are high solubility as well as bioavailability potential for lipophilic and hydrophilic substance. In the present study, 5% ectoin was included to a formulation based on an oil-in-water (O/W) submicron-emulsion, suggesting its topical administration to treat neurodermitic skin. For preparing the O/W emulsion, a membrane emulsification method was examined. Membrane emulsification has received increased attention over the last decade due to its main advantages of obtaining a uniform monodisperse emulsion with a narrow size distribution, at low energy input compared to emulsions prepared by the common methods as homogenizer and high-pressure homogenizer. In comparison to conventional emulsification methods, membrane emulsification may provided more control of the drop size and size distribution. A drop size of 300320 nm with a narrow size distribution was achieved using tubular Al2O3 ceramic membranes (pore size of 200 nm). Based upon the presented results of ectoin permeability into porcine ear skin, it was observed that the application of ectoin into the skin depends on the drop size of the submicron-emulsion.