Static relative permittivities (epsilon(r)) of water + ethane-1,2-diol and water + propane-1,2,3-triol mixtures were measured at the mote fraction of organic component (x(2)) from 0 to 0.8 at 0.2 intervals under pressures up to 300 MPa at the temperature 298.15 K. The relative permittivities at 0.1 MPa (epsilon(r)(P-0)) against x(2) for both aqueous mixtures in this work were correlated with a polynomial equation Of x(2) and were compared with the literature values. The relative permittivities at pressure P (epsilon(r)(P-0)) were also correlated with the polarization (p) for both aqueous mixtures, and reasonable correlations were obtained by use of only one adjustable parameter (k(12)). The experimental E, results as a function of P for each mixture were fitted to a Tait-type equation, and the Tait-type parameters, A and B, were determined. A comparison between composition dependence of (partial derivative In epsilon(r)/partial derivative P)(T) at 0.1 MPa and 298.15 K, (partial derivative In epsilon(r)/partial derivative P)(T,P0), calculated from values of epsilon(r)(P-0) and the Tait-type parameters and that of the isothermal compressibility at 0.1 MPa, K-T,K-P0, was made for both aqueous polyhydric alcohol mixtures. In addition, composition dependence of epsilon(r)(-2)(partial derivative epsilon(r)/partial derivative P)(T) values at 0.1 MPa, epsilon(r)(P-0)(-2)(partial derivative epsilon(r)/partial derivative P)(T,P0), evaluated from epsilon(r)(P-0), A, and B values were correlated with a quadratic equation of x(2). An empirical equation by Marcus for estimating (partial derivative In epsilon(r)/partial derivative P)(T,P0) values was used, and the estimated results were compared with the experimental ones. Furthermore, a combination equation of the correlation equations for epsilon(r)(P-0) and epsilon(r)(p(0))(-2)(partial derivative epsilon(r)/partial derivative P)(T,P0) with x(2) was used to obtain (partial derivative In epsilon(r)/partial derivative P)(T,P0) values, and then it was found that the calculated values reproduce the composition dependence of (partial derivative In epsilon(r)/partial derivative P)(T,P0) well.