A continuous process for producing a rubber-modified methyl methacrylate syrup, which comprises continuously supplying a material liquor comprising 1 to 20 parts by weight of a rubbery polymer dissolved in 100 parts by weight of a monomer comprising 60 to 100% by weight of methyl methacrylate and 0 to 40% by weight of an ethylenically unsaturated monomer copolymerizable with methyl methacrylate, and a radical-polymerization initiator having a half life period of 5 seconds or less at 180.degree. C. or lower to the first reaction zone wherein the starting materials are substantially completely mixed, continuously polymerizing at such a stationary conversion that the rubbery polymer is dispersed in the form of particles, while maintaining the temperature and residence time in the range of 0.5 to 30 minutes in the zone so that a steady-state is achieved in the zone and the steady-state concentration of the initiator in the reaction mixture is 1/2 to 1/1,000 time as much as the concentration of initiator supplied, continuously taking out the resulting reaction mixture from the zone, and passing it through the second reaction zone having a volume of 0 to 5 times as much as that of the first reaction zone wherein a piston flow is substantially achieved, and thereby the final concentration of the initiator being decreased to obtain a stable syrup comprising a disperse phase and a continuous phase, the former phase being a solution of a major amount of the rubbery polymer and a minor amount of the resinous polymer in the monomer, the latter one being a solution of a major amount of the resinous polymer and a minor amount of the rubbery polymer in the monomer, the average particle diameter of the disperse phase of the syrup being in the range of 0.1 to 20.mu. and the number average polymerization degree of resinous polymers in the continuous phase of the syrup being within a range of 300 to 6,000, and the conversion of monomer to polymer of 5 to 40% being achieved.