The present invention relates to an impact resistant resin composition having superior balance of physical properties of chromacity, impact resistance and strength, and a process for preparing an impact resistant resin composition that can largely reduce draining treatment. The process of the present invention comprises the steps of preparing a resin without rubber ingredient by a mass polymerization, and adding and mixing a conjugated copolymer having rubber ingredient, when the resin is molten in the latter part of monomer-removal process, to prepare an impact resistant resin composition, wherein the conjugated copolymer is previously dehydrated and dried by filtering a copolymerization liquid.