NaYF4∶Tb3+, Yb3+ down-conversion (DC) phosphors were synthesized by hydrothermal method. X-ray diffraction (XRD), photoluminescence (PL) and photoluminescence excitation (PLE) spectra were used to characterize the samples. Experiment results revealed that samples of NaYF4∶Tb3+, Yb3+ crystallized in hexagonal shape without cubic shape. When the doping concentration of Tb3+and Yb3+ was altered, the lattice structure of samples did not change, indicating that the Tb3+ and Yb3+ ions are completely dissolved in the NaYF4 host lattice by substitution for the Y3+. The emission from 5D4→7F6(489 nm), 5D4→7F5(542 nm), 5D4→7F4(584 nm), and 5D4→7F3(619 nm) of Tb3+ ions was observed, in which the dominant emission was at 542 nm. With single Tb3+ doping, no near-infrared (NIR) emission was observed under excitation of 355 nm pulsed laser. However, while with Tb3+ and Yb3+ codoping, the NIR emission at around 950～1 100 nm from Yb3+(2F5/2→2F7/2) was observed under the same excitation. The dependence of the visible and NIR-emissions on Yb3+ doping concentration has been investigated. These results show that there is energy transfer process between Tb3+and Yb3+. Furthermore, it is a possible DC process through cooperative energy transfer from Tb3+ to Yb3+. When the doping concentration is 1% mol Tb3+ and 6% mol Yb3+ respectively, the intensity of NIR emission reaches its strongest.