Polystyrene latex and precipitated calcium carbonate (PCC) with and without dextran sulfate pretreatment were flocculated by the consecutive addition of high-molecular-weight poly(ethylene oxide) and a novel composite latex microparticle consisting of a polystyrene core and a poly(p-vinylphenol) shell. Good flocculation of polystyrene latex and PCC was obtained, whereas the PCC coated with dextran sulfate was not flocculated. The interaction of the composite microparticle with the target colloids was governed by electrostatic forces, whereas hydrogen bonding and hydrophobic interactions drove the PEO adsorption onto the composite particles.