A process is disclosed for the continuous production of an ABS resin. The polymerization step comprises at least two substeps, one being a first-stage substep of forming particles of the rubbery polymer and the other a second-stage substep of adjusting the particle sizes of the particles. The first-stage substep is conducted in a polymerization system making use of a plug flow reactor or a batch polymerization reactor, and conducts polymerization at least until the particles are formed in the polymerization mixture. The second-stage substep increases a converted amount of the monomer component into the polymer compared with that in the particle forming substep and makes the particles smaller. A polycarbonate-ABS resin composition is also disclosed.