Nasicon type compounds of general formula Ca0.5SbMP3O12 (M = Al, Fe, Cr) are prepared by solid-state method. All the compounds crystallize in hexagonal lattice with R(3) over bar c space group. The IR spectra show characteristic PO4 vibrations. Conductivity studies indicate the presence of charged defects. The Cole-Cole plots of impedance are semicircles between 150 and 350 degrees C. The thermal expansion of these samples is studied in the temperature range 25-500 degrees C.