A co-precipitation method for synthesizing Gd2O2S:(Yb3+,Er3+) nano-particles was developed, using the commercially available Gd2O3, Er2O3, Yb2O3, H2SO4 and NaOH as the starting materials. XRD analysis shows that the precursor can be transformed into single phase Gd2O2S nano-particles by calcining at 900 °C for 1 hour in hydrogen atmosphere. TEM observation shows that the Gd2O2S particles are quasi-spherical in shape and well dispersed, with a mean particle size of about 20-30 nm. Under 980nm infrared light excitation, the strongest emission bands of Gd2O2S:Er3+ nano-particles located at green region centered at 525 nm and 550 nm, attributing to the 2H11/2→4I15/2 and 4S3/2→4I15/2 transitions of Er3+ ions, respectively. The quenching concentration of Er3+ ions is 5 mol%. The up-conversion luminescent intensity increases obviously for Yb3+ and Er3+ co-doped Gd2O2S:(Yb3+,Er3+) nano-particles.