The B3PW91 method of the density functional theory has been applied to the study of the dipole polarizability of medium size silicon clusters employing pseudopotential on all of them. All electron calculations have been performed for those clusters with less than nine atoms. In addition, we have optimized the structures of the clusters with less than ten atoms. On using the modified genetic algorithm, fourteen conformers of silicon isomers with nine atoms have been determined. The corresponding geometry of these clusters was optimized and their relative stability determined. The calculated polarizabilities are compared with experimental data and previous theoretical results.