A modulated differential scanning calorimetry (MDSC) method combining transmission electron microscopy (TEM) for characterizing the morphology of composite latex particles has been developed. Sulfortated polystyrene (S-PS)/poly(methyl methacrylate) (PMMA) (50:50 by weight) composite latex particles were prepared as model samples. PS particles were prepared by self-emulsification using lightly S-PS in co-solvents/water. For the preparation of S-PS/PMMA composite latex particles, the guest methyl methacrylate (MMA) monomers first diffused into swollen S-PS particles in S-PS aqueous dispersions, and then the MMA monomers were polymerized. Based on the MDSC method, one can determine quickly whether and what kinds of composite latex particles are prepared. Combing TEM, morphological parameters, such as the radius of core, diffused-phase thickness and thickness of shell of the composite latex particles, can be obtained. (C) 2004 Elsevier B.V. All rights reserved.