The dielectric, pyroelectric and piezoelectric properties of relaxor ferroelectric in the 0.69(Pb(1–3x/2)Bix)(Mg1/3Ta2/3)O3-0.31PbTiO3 ceramics have been investigated. The dielectric constant and loss of poled ceramic samples were determined. The pyroelectric coefficient and the spontaneous polarization were measured by the static Byer-Roundy method as a function of temperature. The piezoelectric d33 and coupling factor (kp) were measured by using the Berlincourt d33 meter and resonance-antiresonance method, respectively. The Curie temperature and pyroelectric peak temperature decreased gradually with the addition of Bi2O3. The maximum dielectric and pyroelectric constant increase sharply with addition of 1 mole% Bi2O3 and then decrease gradually with further addition of Bi2O3. The PMT-PT specimen modified 3 mole% Bi2O3 showed a large voltage responsivity (Fv ∽ 0.1m2/C). The dissipation factor and piezoelectric constant could be improved by small additions of Bi2O3.