||This study introduces a new Janus colloid surfactant system exhibiting remarkable catalytic activities and magnetic responsiveness in Pickering emulsion microreactors. Patching of catalytic nanoparticles (NPs), such as Pd NPs and Ag NPs, on amphiphilic Janus microparticles (JMPs) endows the controlled catalytic activities for organic reactions at the reactant-water interfaces. Through three model organic reactions, including oxidation, amination, and reduction, we figure out that the JMP catalysts assemble at the reactant-water interfaces of Pickering emulsion droplets and play an essential role in enhancing the reaction kinetics. Moreover, when Fe2O3 NPs were site-specifically co-patched, the produced emulsion droplets show magnetic responsiveness, thus leading to facile recovery of products and effective recycling of JMP catalysts. The colloid surfactant catalysts developed in our study are expected to advance the environment-friendly catalyst system for green chemistry.