We present a facile approach to produce submicrometer sized Janus PAN/PS polymer colloids by seeded emulsion polymerization. Both high cross-linking degree and slow feeding monomer are crucial to control the resultant anisotropic structure, The PAN seed is cross-linked, ensuring that the formed PS bulge contains no PAN, The two different polymers are distinct compartmentalized onto the surface. Other Janus composite colloids with varied composition and microstructure are derived by selective modification of desired polymer part and following favorable growth of other materials therein. The Janus colloids can serve as solid surfactants to emulsify oil/water immiscible mixtures, which have a well-defined orientation at the interface. The method can be scaled up to produce large quantity of submicrometer sized Janus colloids.