Static relative permittivities (is an element of(r)) of water + propane-1,2-diol and water + propane-1,3-diol were measured at four mole fractions under pressures up to 300 MPa at 298.15 K. A Tait-type equation was used to represent is an element of(r) with pressure (P) for each composition. Values of (partial derivative ln is an element of(r)/partial derivative P)(T) and is an element of(r)(-2)(partial derivative is an element of(r)/partial derivative P)(T) at 0.1 MPa for both aqueous propanediol systems were determined by use of the static relative permittivity at 0.1 MPa, is an element of(r)(0.1 MPa), and the Tait-type parameters, A and B. Values of (partial derivative ln is an element of(r)/partial derivative P)(T) and the isothermal compressibility (kappa(T)) at 0.1 MPa over the entire composition range are compared for both aqueous propanediol systems. A relationship between (partial derivative ln is an element of(r)/partial derivative P)(T) and kappa(T) at 0.1 MPa was derived from the density dependence of is an element of(r). Furthermore, composition dependence of is an element of(r)(-2)(partial derivative is an element of(r)/partial derivative P)(T) at 0.1 MPa was examined for the present systems.