La2O2S:Eu3+ nanocrysytals (NCs) with a mean size of 18 nm are prepared by gel thermolysis. The morphology of the particles is hexagonal. The surface Eu3+ ions are first detected by time-resolved spectra in the D-5(0) -> F-7(1) region. Because the symmetry of the sites occupied by surface Eu3+ ions is lower, the D-5(0) -> F-7(1)(E) line, which is doubly degenerate in the bulk crystal, is split, and the fluorescence lifetime becomes shorter. The results of the laser-selective excitation indicate that the degradation of the site symmetry of Eu3+ seems to be abrupt, which means the as-synthesized La2O2S:Eu3+ NCs might be of the La2O2S/La2O2-xS1+x core-shell structure and the shell are not in a disordered state but a rather pure one.