The sintering behavior, microstructure and microwave dielectric properties of BiNb1-xMoxO4 (x=0.005, 0.01, 0.03 and 0.05) ceramics have been investigated. The phase-forming temperature (from orthorhombic to triclinic phase) of BiNb1-xMOxO4 ceramics during sintering is lower than that (1024 degrees C) of BiNbO4 ceramics. The variations of dielectric constant, Q value and temperature coefficient of resonant frequency are also investigated. A defect dipole model is proposed for the explanation of dielectric behavior of MoO3 -doped BiNbO4 ceramics. (c) 2006 Published by Elsevier B.V.