The chemical polymerization of aniline was carried out in methylene chloride/water media by use of benzoyl peroxide as an oxidant. To obtain PANI emulsion, PANIs nanoparticles has been prepared in aqueous solution by chemical oxidation using emulsification diffusion method. This method enable to obtain effect of the size reduction. The particle size varied with the ratio of methylene chloride/water and the average size of PANI particle determined by scanning electron microscope (SEM) was 40-50 nm and the green colored colloidal emulsion have a long-term colloirdal stability and exist as stable emulsion without any precipitation.