The temperature-dependent quenching characteristics of the upconversion luminescence in NaYF4:Yb3+,Er3+ nanoparticles under 980-nm excitation are reported. Intense green and red upconversion emissions corresponding to the (H-2(11/2), S-4(3/2)) -> I-4(15/2) and F-4(9/2) -> I-4(15/2) transitions of the Er3+ ions were observed. The green emission at around 520 nm presents a continuous increase with increasing temperature, while the emission bands at around 545 and 657 nm decrease with the temperature change from 84 to 364 K. The temperature dependence of the intensity characteristics was analyzed systematically by using a simple three-level system.