The dielectric constant is one of the basic electrical properties of solids. Dielectric properties are correlated with the electro- optic property of the crystals 120l. Crystals with high transparency and large surface, defect-free (i.e. without any pit or crack or microscope), grown scratch on the surface, tested with a traveling died by the slow cooling method were used for the dielectric measurements. The size of the crystals was 6 mm x 6 mm x 2mm. samples were coated with good-quality graphite to obtain a good FTIR conductive surface layer. The capacitance (Corys) and dielectric loss rent factor (tan 5) were measured using the conventional parallel plate in capacitor method with a fixed frequency pof 1 kHz using Agilent ranging from 313 to temperatures KDP 4284A LCR meter at various were done on a-b directions of the 423 K. The measurements ns crystals. The samples were annealed up to 423 K to remove water The molecules if present. The observations were made while cooling FTIR the sample. Air capacitance (Cair) was also measured. The in dielectric constant of the crystal was calculated using the relation