Densities and viscosities of the binary mixtures of acetic acid + acetic anhydride have been measured at temperatures from (293.15 to 338.15) K and atmospheric pressure over the whole concentration range of compositions. The excess molar volume (V(E)) and viscosity deviation (Delta(n)) were calculated from the experimental data and correlated by the Redlich-Kister equation. In addition, densities and viscosities of methenamine + acetic acid solutions were measured, and the results were represented by third-order and fourth-order (empirical) polynomials in terms of mole fraction of methenamine.