A method for preparing polymer latex particles having a core/shell structure includes the steps of: forming a dispersion of colorant; heating and mixing an organic phase comprising core monomers and wax to form a blend of the wax and monomers; mixing the dispersion of colorant with the blend of wax and monomers, and adding a first polymerization initiator for forming the core to the resultant mixture to perform polymerization, thereby forming core polymer particles comprising the wax and colorant; and mixing shell-forming monomers with the polymer particles comprising the wax and colorant, and adding a second polymerization initiator for forming the shell to the resultant mixture to perform polymerization, thereby forming a shell layer on the core polymer particles, wherein the colorant is a pigment, and the polymerization initiator for forming the core includes an azo-based polymerization initiator. The method is cost-efficient because the core/shell polymer latex particles are prepared by a simple emulsion polymerization process, with no need of additional cohesion or melting processes. Additionally, when the core/shell polymer latex is used in a polymer composition, it is possible to improve a bonding degree between heterogeneous particles of a colorant, wax and latex and distribution uniformity of the particles, and thus to control the content of each component with ease.