We report the preparation of silicon nanocrystals with efficient ultraviolet luminescence by nanosecond pulsed laser ablation in de-ionized water at a high laser fluence condition. Atomic force microscopy results show that nano-grains form in the process of laser ablation. Fourier transform infrared spectroscopy analyses indicate that silicon nanocrystals are formed and partially oxidized during synthesis. The photoluminescence measurement and the ultraviolet-visible transmittance spectroscopy of the samples prepared at various fluences reveal that all the prepared samples present an efficient ultraviolet emission at room temperature and it can be attributed to the quantum confinement effect and surface defect states. The emission wavelength of silicon nanocrystals is far shorter than visible light, which means potential applications in optoelectronic devices.