YLiF4 :Er3+, Yb3+ was synthesized by hydrothermal method. The concentration of Er3+ was 2 mol%, and Yb3+ changed from 0 to 7 mol%. At room temperature the absorbance of YLiF4: Er3+, Yb3+ in all samples was measured from 200 to 1 200 nm. The absorbance around 980 nm increased with increasing Yb3+ concentration. The result shows that the upconversion intensity excited at 980 nm was enhanced. The enhanced intensity is dependent on the Yb3+ concentration. The excitation spectra and photoluminescence spectra were measured in the sample with Yb3+ concentration of 2 mol%. The red and green luminescence came from the transition 4F(9/2) --> 2 I(15/2), and 4 S(3/2) -->2 I(15/2) and 2H(11/2) --> 2 I(15/2), respectively.