A new apparatus was designed with a thick-walled glass capillary, electric heater tube with red copper and heat preservation. The thick-walled glass capillary was used for its advantages of resistance to acid corrosion and pressure, and ease of observation. The experimental densities over the entire range of mole fraction for the binary mixture of p-xylene+acetic acid and o-xylene+acetic acid were measured using the new apparatus at temperatures ranging from 313.15K to 473.15K and pressure ranging from 0.20 to 2.0 MPa. The-density values were used in the determination of excess molar volumes, V-E. The Redlich-Kister equation was used to fit the excess molar volume values, and the coefficients and estimate of the standard error values were presented. The experimental results prove that the density measurement apparatus is successful.