Electrospraying (electrohydrodynamic spraying) is a method of liquid atomization by means of electrical forces. In electrospraying, the liquid flowing out of capillary nozzle, which is maintained at high electric potential, is forced by the electric field to be dispersed into fine droplets. The process start with onset and emission which is followed by columbic explosions leading to further breakdown of droplets until they reach collector. Droplets can be extremely small, in special cases down to nanometers. The charge and size of the droplets can be controlled to some extent by voltage, concentration, flow rate of the liquid at the capillary nozzle and gauge of needle. Spraying solution or suspensions allows production of fine particles, down to nanometer size. Nanometer sized particles are of considerable interest for a wide variety of applications, because the chemical and physical behavior of the particles is unprecedented and remarkably different from those in bulk form. Due to small size and extremely large specific surface area are useful for microencapsulation, chromatography, catalyst, organic/inorganic hybrid materials, and templates for porous inorganic materials. Knowledge of the nanoparticle size and it’s distribution is important for the interpretation of experimental result in many studies of nanoparticle properties; for example, magnetic recording media, ferro fluids, catalysts and in biotechnology. In this research the effect of material and process parameters on electrosprayed polyacrylonitrile particles size was modelled. Acrylonitrile is a commonly used monomer for producing acrylic fiber and also acts as comonomer in the synthesis of engineering plastics because of its high chemical resistance, barrier property, and high reactivity with other monomer such as vinylidene chloride and styrene. To model the electrosprayed polyacrylonitrile particles size, a factorial design was employed and finally a polynomial model was represented by response surface methodology(RSM). For modeling four factors namely; applied voltage, solution concentration, volume flow rate and diameter of syringe needle were chosen, each at three levels. The choice of three levels for each factor in the experimental design allowed us to take advantage of quadratic models. At first full factorial experimental design at three levels of each factor was carried out, and the ANOVA analysis is used to study the treatments. Then, values for coefficients, P-values and R2 for response surface model are obtained by regression analysis. Response surface method is a collection of mathematical and statistical techniques that are used to model and analyze engineering applications. The response surface method is applied to situations where several input variables potentially influence some performance or characteristics of the process that often called response. The relationship between the response (y) and k input variables could be expressed in terms of mathematical notation. The ANOVA analysis showed that all main effects of four factor and interaction of applied voltage and flow rate were found statistically significant in the mean of electrosprayed polyacrylonitrile particle size(p-value 0.05). Finally, the mean size of nanoparticles was modeled by RSM as a functions. In represented model, the R2 values is about 0.80, illustrating that the model is able to explain 80.2% of the variability in the mean particle size.