Nano europium oxide cyclohexanone colloids were prepared by pulsed laser ablation of the Eu2O3 target submerged in flowing liquid containing cyclohexanone and phthalic anhydride. The colloids were characterized by fluorescence spectra, fluorescence lifetime, high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SED). The results show the nanoparticles in the colloids have the structure with Eu3+ ions located in the core and Eu2+ ions at the surface of nanoparticles. Phthalic anhydride coordinates to the surface europium ions and reduces Eu3+ ions to Eu2+ ions. Phthalic anhydride and cyclohexanone can absorb UV radiations and transfer the energy to the surface Eu2+ ions; and then Eu2+ ions emit violet fluorescence with intense emission peaks at 415 nm and 465 nm, respectively, which can be ascribed to the lowest 5d-4f transition of Eu2+ in europium oxide nanoparticles.