Poly(methyl methacrylate) (PMMA)/polystyrene (PS) and poly(butyl acrylate) (PBA)/PS composite latices were prepared by surfactant-free, two-stage emulsion polymerization with potassium persulfate as an initiator, and the particle morphology of thus synthesized composite latices was studied. The heterogeneous morphologies, such as raspberry and confetti-like, were observed ; (1) when less hydrophilic PS was polymerized in the second stage onto more hydrophilic PMMA core or (2) PS was polymerized in the second stage onto hydrophobic core, PBA, which has T_g value much lower than reaction temperature(70℃). Transformation of latex morphology occurred to a higher degree when molecular weight or viscosity of core polymer was low, possibly due to increased mobility of core polymer molecules.