The stability of the silver iodide and iron(lll) oxide dispersions has been investigated in the presence of monoamino-monocarboxylic acid, neutral amino acid. The critical coagulation concentrations of the dispersions, Ccincreased with increasing amino acid concentration and then decreased. The optimum amino acid concentration for the stabilization decreased with increasing number of carbon atoms of amino acid. The results indicate that the stabilization of the dispersions by amino acids is due to the adsorption of amino acids onto the particles. The stabilizing effect is discussed in terms of the total potential energy of interaction between the particles which was calculated by considering the existence of the adsorbed layers on the particles using the experimentally determined Hamaker constants and outer Helmholtz plane potentials.