Polycrystalline samples of Pb(Mg 1 / 2 X 1 / 2 )O 3 (X=Mo and W) were synthesized by a high-temperature solid-state reaction technique. Preliminary structural (X-ray diffraction) study of the compounds shows the formation of a single phase compound. Microstructural study of the compounds shows a uniform distribution of nearly spherical grains throughout the surface of the sample. Detailed studies of relative dielectric permittivity ( r ) and loss tangent (tanδ) of the compounds both as a function of frequency (10 2 -10 4 Hz) at room temperature (30 o C) and temperature (30-320 o C) at 10kHz suggest that the compounds have antiferroelectric phase transition. The activation energy of the Mo and W containing compound was found to be 0.61 and 0.72eV, respectively.