Solid lipid nanoparticles (SLN) are colloidal lipid carriers, which used for improving the bioavailability of lipophilic and hydrophilic drugs. SLN are composed of biodegradable lipids such as hard fats, highly purified triglycerides, monoglycerides, complex glyceride mixtures or waxes which are solid at room temperature. In the present study, different formulation variables, including the type and quantity of lipid and surfactant were optimized for the preparation of SLN. SLN were prepared by a modified micro emulsion-based method and their particle size was evaluated. Two types of surfactants Tween 80 and Poloxamer 188 were used. Also, the monoglyceride (Glyceryl monostearate) and wax (Cetyl palmitate) were used as lipid. The optimum SLN formulae were at lipid concentration 5%. The optimum surfactant concentration was 6%. SLN with a surfactant Tween 80 were smaller in size than Poloxamer 188 SLN. Glyceryl monostearate formed a smaller size SLN than Cetyl palmitate. Increasing Glyceryl monostearate concentration in the lipid ratio resulted in the formation of small size SLN.