Complex permittivity measurements of 12-tungstophosphoric acid hexahydrate (WPA . 6H(2)O) have been performed in the X-band region at room temperature. Permittivity data were obtained by measuring reflection (S-11) and transmission (S-21) parameters with a network analyzer and also by using a short-circuited-waveguide. Results on powder samples are compared with the results on compressed samples using the model of mixtures. From Cole-Cole plots, a dipole relaxation lime tau = 1.9 x 10(-11) s was determined and attributed to polyatomic ion reorientation.