Experimental liquid viscosities of pure compounds and their mixtures are needed for the design of chemical processes in heat and mass transfers or fluid mechanics. This paper is about partial work supported by SNOPEC (China Petroleum & Chemical Corporation). The results are related to the design calculation of synthesis of purified terephthalic acid (PTA). At temperature (313.15 to 473.15) K, the viscosities of pure p-xylene, pure acetic acid, and the p-xylene + acetic acid binary system of different concentrations were determined by a rolling-ball viscometer at pressures (0.10 to 3.20) MPa. Then, the viscosity data were fitted by a correlation equation. The AAD of the correlation is 1.21 %.