This paper deals with the investigation on the influence of four amphiphile monolayers viz. arachidic acid, a mixture of dioctadecyl amine and arachidic acid (3:1(, carboxybetaine and dioleoyl-L-a-lecithin (DOPC) on ammonium nitrate crystallization. The study was carried out by means of surface pressure vs. area, surface potential vs. area and fluorescent microscopy. Results indicated a strong effect on ammonium nitrate crystallization in the presence of carboxybetaine and dioctadecylamine monolayers, whereas an inhibition in crystal growth was observed in the presence of DOPC.