Yb3 , Er3 -codoped YF3 nanoparticles were rapidly prepared via microemulsion method at room temperature. The nanoparticles were characterized by x-ray diffraction(XRD) and scanning electron microscopy(SEM). The XRD pattern matched well with card PDF#74-911. SEM patterns indicated that the nanoparticles were spherical morphology with the average size about 32 nm. Downconversion spectrum and upconversion spectrum were investigated. It was found that the predominant emission peak of downconversion spectrum was located at 1544 nm. In the upconversion spectrum, the intensity of red emission was stronger than that of green. In this material, both the red and green emissions were due to two photon processes. Meanwhile, upconversion mechanism and process were also analyzed.