A method is developed for the preparation of mixed pentoxide Nb2(1–y)Ta2yO5 by rapid coprecipitation of a mixture of hydroxides of niobium and tantalum from a solution of hydrofluoric acid by ammonia water, followed by purification and calcination of the precipitate. The proposed method allows obtaining a homogeneously mixed pentoxide of niobium and tantalum Nb2(1–y)Ta2yO5, in contrast to the method of obtaining Nb2(1–y)Ta2yO5 from a mechanical mixture of individual pentoxides of niobium and tantalum. The temperature dependences of the real part of the permittivity (ε′) of ceramic samples of Nb2(1–y)Ta2yO5 at various frequencies were investigated and the magnitude of dielectric loss (tan(δ)) versus frequency measurement of the electric field and temperature was evaluated. On the basis of analysis of the data of impedance spectroscopy, the temperature dependence of the static conductivity σdс of the ceramic Nb2(1–y)Ta2yO5 was determined. From the temperature dependence of σdс, the enthalpies of activation of charge transport for different temperature ranges were evaluated.