The efficient functionalization of poly(divinylbenzene) (polyDVB) nanoparticles via Paterno-Büchi type [2 + 2]-photocycloadditions is described. Initially polyDVB nanoparticles with high density of alkene groups on the surface are synthesized via radical miniemulsion polymerization. Subsequently, UV-induced [2 + 2]-photocycloadditions with different functionalized aldehydes have been performed on the surface under mild and catalyst-free conditions. In order to show the versatility and the accessibility towards incorporation of different functionalities with this strategy, surface modifications were carried out with ATRP initiators and NHS esters for bioconjugation, respectively. Finally, these photofunctionalized nanoparticles were grafted with poly(butyl acrylate) or with gold-labeled antibodies to prove the success of the reactions. PolyDVB nanoparticles before and after photofunctionalization are characterized by X-ray photoelectron spectroscopy (XPS), electron microscopy (SEM and TEM) and ATR-FTIR spectroscopy. Results show that the photoconjugation route is highly efficient and grafting densities of 4 to 5 molecules per nm2 on the entire surface of the particles are achieved.