Dielectric relaxation dynamics properties of 5CB (4-cyano-4-pentylbiphenyl) and BAC(4-[4-(S)-2-methylbutoxybenzoyloxy]benzoic acid) have been investigated. In this respect, dielectric properties of 5CB plus (1%)BAC have been compared with 5CB. The polarizing microscopy results show that BAC and 5CB exhibit enantiotropic N* mesophase and N mesophase, respectively. The real (epsilon ') and imaginary components (epsilon '') of dielectric constant have been calculated by capacitance method. The dielectric relaxation mechanisms of liquid crystals have been analyzed by Cole-Cole plots and the Debye distribution parameters (alpha) have been calculated. It has been also determined that adding BAC to 5CB increases the voltage dependent dielectric strength.