Urushiol, the main component of the natural product of raw lacquer, can react with ester easily owing to its two adjacent phenolic hydroxyls, and urushiol-ester compounds can polymerize further attributing to its unsaturated side chain. In this work, poly(urushiol borate) (PUB) was coated on the surface of polystyrene (PS) microspheres by transesterification between urushiol and tributyl borate. Then, the core-shell composite microspheres of polystyrene@poly(urushiol borate) (PS@PUB) were obtained. Finally, we used a general method to synthesize anisotropic grenade-like Janus composite particles of PUB/PS, that is, the core-shell composite microspheres of PS@PUB were swelled assisted protrusion in the emulsion of organic monomer and water. The morphologies of PUB/PS Janus composite particles could be tuned by changing the swelling time and the dosage of organic monomer. POLYM. ENG. SCI., 58:2304-2310, 2018. (c) 2018 Society of Plastics Engineers