A method for preparing a masterbatch of synthetic elastomer and of carbon-based filler, which comprises the following steps: preparing an aqueous dispersion of carbon-based filler having a zeta potential with the opposite sign to that of an anionic or cationic synthetic elastomer latex, the difference between the potentials of the anionic or cationic elastomer latex and the aqueous dispersion of carbon-based filler being such that the absolute value thereof is greater than or equal to 20 mV, bringing together, and mixing, the anionic or cationic synthetic elastomer latex and the aqueous dispersion of carbon-based filler to obtain a coagulum, recovering the coagulum, and drying the recovered coagulum in order to obtain the masterbatch.