Here we report the design of well-dispersible conjugated microporous polymer nanoparticles as highly stable heterogeneous organic photocatalysts in aqueous medium. This class of materials combines two different heterogeneous catalytic model systems: (i) nanostructured catalysts and (ii) highly porous materials. By incorporating different electron donor and acceptor moieties, the nanoparticle shape can be controlled ranging from nanospheres via nanorods to nanorings. The high photocatalytic activity, stability and reusability of the materials were demonstrated in the reductive activation of molecular oxygen and photooxidation of amines under irradiation of a household energy-saving light bulb.