The coalescence process of polymer latex particles has been investigated by following simultaneously weight losses and dielectric constants variations during water evaporation in a latex deposited as a film in a resonant cavity at microwave frequency (5 GHz) and under controlled humidity and temperature. Different styrene (S) n-butyl acrylate (BuA) emulsion copolymer latexes were examined so as to differentiate the behaviors of film forming or non-film-forming latexes. In the latter ones, both flocculation and maximum packing points were clearly evidenced, whereas only the first point was shown in the former ones. The effect of other colloidal variables (particle size distribution, surface charge density, particle diameter, ionic strength) have also been studied. It is found that the influence of the last three parameters is reflective of the latex stability and can be well detected by dielectric measurement. Such a method appears to be quite reliable for studying the film-forming process of latexes having different colloidal characteristics.