The density of 1-ethyl-3-methylimidazolium nitrate and 1-ethyl-3-methylimidazolium methylsulfate were measured by MDY-2densimeters at various temperatures. The results showed that the density of Ionic liquids is a linear decrease with the increase of temperature. The coefficients of thermal expansion α of the two ionic liquids were obtained by calculating from the experimental density values. The values of α were 6.75×10-4 K-1and 5.79×10-4 K-1, respctively. At 298.15K and 313.15K, molecular volumes, standard entropies and lattice energy of these ILs were also discussed.