Ferulic acid (4-hydroxy-3-methoxycinnamic acid), an effective component of medical plant, is a phenolic acid with low toxicity that can be absorbed and easily metabolized in the human body. The solubility of Ferulic Acid (FA) is very low in aqueous solutions which can cause problem in preparation of pharmaceutical products, but it can easily be dissolved in oil/water interface of nano-emulsions. In the present work, a kind of ferulic acid nano-emulsion was prepared using the spontaneous Emulsification method which occurs when an organic phase and an aqueous phase are mixed. A chemometrics approach has been used to optimize the size of FA nanoemulsions. The experiments were performed according to a Box-behenken experimental design, one of the most suitable experimental design for modeling studies. The effect of three experimental parameters on droplet size was studied using multivariate analysis. The factors studied and the related levels were the concentration of lecithin (0.7-2 % w/w, in aqueous phase), the concentration of tween-80 (2-8 % w/w, in aqueous phase) and sounication time (10-45 minutes). In all the experiments, the water phase was added to the organic phase including lecithin, tween-80 and FA in ethanol solvent. Then experimental droplet sizes were fitted to the polynomial model. Good descriptive and predictive ability of the model was verified as high values of the statistics R2 (0.996) and F (112.5) were obtained for the linear relationship between predicted and experimental values of the dependent variable.