The viscosities of pure water, the acetic acid + water binary system, and the p-xylene + acetic acid + water ternary system at different concentrations were determined with a rolling-ball viscometer at temperatures from 313.15 to 473.15 K and pressures from 0.10 to 3.20 MPa. The viscosity data were fitted by a correlation equation for the estimation of the mixture viscosities. The average absolute deviations (AAD) of the correlation for binary and ternary systems are 2.48% and 1.77%, respectively.