We prepared a Y2O3:Er,Yb nanoparticles by laser ablation in liquid. The laser used the second harmonic generation Nd:YAG (532 nm). A preparation process and measurement of upconversion properties were performed by varying the range of the energy density of the laser. Images from scanning electron microscopy (SEM) indicated that two types of nanoparticles existed in the product of laser ablation in liquid. We concluded the following:one type of nanoparticles was prepared from the nucleation of materials in a plume and the other was prepared by fragmentation. In the photoluminescence spectra, green (H-2(11/2), S-4(3/2)-->I-4(15/2)) and red (F-4(9/2)-->I-4(15/2)) fluorescence were observed using a 980 nm laser diode (LD) as the excitation source. We confirmed that the fluorescence intensity increased with increasing energy density of the laser. Thus, we concluded that the number of the nanoparticles increased as the energy density of the laser was increased. (C) 2012 Elsevier B.V. All rights reserved.