ZrO2∶Er3+/Yb3+/Li+ nanocrystals are synthesized by sol- gel method. Li+ ions doped in ZrO2∶Er3+/Yb3+ nanocrystals can greatly enhance the upconversion luminescence intensity of Er3 + ions. And the effect of Li+ ions on enhancement of upconversion luminescenceis is discussed. The fluorescence intensity ratio of the green upconversion luminescence bands and that of the green upconversion luminescence peaks are studied as a function of temperature in a range of 303 K~753 K. The maximum sensitivity is approximately 0.0050 K- 1 at 440 K by adopting the fluorescence intensity ratio of green upconversion luminescence peaks at 525 and 562 nm . It suggests that ZrO2∶Er3+/Yb3+/Li+ nanocrystals is a suitable probe for optical temperature sensing by the fluorescence intensity ratio technique.