re those associated with the conditions of adding the organic phase to the aqueous phase, such as organic phase injection rate, aqueous phase agitation rate, the method of organic phase addition and the organic phase to aqueous phase ratio. Lince et al.,2008 [175] indicated that the process of particle formation in the nanoprecipitation method includes three stages: nucleation, growth and aggregation. The separation between the nucleation and the growth stages is the key factor for formation of uniform particles. Ideally, operating conditions should allow a high nucleation rate strongly dependent on super saturation and low growth rate. Nanoprecipitation method has some advantages over other method used for preparation of nanoparticles, which include that: (1) Major advantage of this method is the use of the solvents (Acetone/Ethanol) which are considered to be less toxic than water- immiscible solvents like dichloromethane and chloroform, (2) in this method, nanoparticles are formed spontaneously with high shear , (3) Further purification is not required because of the surfactant and solvent and (4) it is a simple, fast and reproducible method which is commonly used for the preparation of both nanocapsules and nanospheres. The solvent displacement technique can be used to formulate nanocapsules by incorporating a small amount of nontoxic oil in the organic phase. Considering the oil-based central cavities of the nanocapsules, high loading efficiencies are usually obtained for lipophilic drugs when nanocapsules are prepared. The major drawbacks of this preparation method include that: (1) the use of this simple method [176] is restricted to water-miscible solvents, in which the diffusion rate is sufficient to produce spontaneous emulsification. In some cases, spontaneous emulsification is not ob>