Urushiol praseodymium-polystyrene (UPr-PS) Janus composite particles were synthesized by emulsion swelling assisted protruding from UPr/PS core-shell composite microspheres. The effects of sulfonated time and the outer electronic configuration of metal on the shell of urushiol metal/PS composite microspheres, together with the effects of monomer type, monomer dosage and swelling time on the swelling behaviour, were studied. The morphology, chemical composition and thermal performance of UPr/PS core-shell composite microspheres and UPr-PS Janus composite particles were studied by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analyzer (EDX), Thermogravimetric analysis (TG) and infrared spectrometer (IR). Results showed that the morphology could be controlled by the metal kind, the sulfonated time, the monomer type, the monomer dosage and the swelling time. Attributing to the novel anisotropic structure, the UPr-PS Janus composite particles will be expected to be applied in oriented catalyst. POLYM. ENG. SCI., 59:411-417, 2019. (c) 2018 Society of Plastics Engineers