Beta-iron disilicide beta -FeSi2 polycrystals were synthesized by the horizontal gradient freeze method, and beta -FeSi2 single crystals were grown by the chemical vapor transport method using polycrystals as the starting material and iodine as a transport agent. The beta -FeSi2 polycrystals and single crystals were characterized by optical measurements. The Raman and infrared active optical phonons were observed by Raman scattering and optical reflection measurements, respectively. The dielectric constants were calculated by Kramers-Kronig transformation of the optical reflection spectrum. The small polaron reflecting LO phonon of beta -FeSi2 was discussed by Frohlich's model using the obtained dielectric constants.