Abstract: A stable aqueous emulsion of an acrylonitrile polymer which comprises a dispersion system of said acrylonitrile polymer having a particle size of substantially less than 1.mu. in water and contains substantially no emulsifying agent nor dispersing agent. Said emulsion is produced by a process comprising; polymerizing acrylonitrile alone or in a monomer mixture comprising more than 60% by weight of acrylonitrile and as another component, at least one other ethylenically unsaturated compound, under stirring at a temperature higher than 120.degree. C and at least autogenous pressure, in an aqueous system consisting essentially of water in an amount of 45 to 95% by weight based on the total weight of water and monomer(s), to thereby introduce at least 2.times.10.sup.