Spectral investigations of the new organic metal β-(EDT-DTDSF) 4 Hg 3 I 8 were performed. Polarized reflectance (from 500 to 17000cm −1 ) and Raman spectra of single crystals were studied at room temperature. An electronic dispersion in IR spectra was analyzed versus temperature (from 4 to 300K) in terms of the Drude model and optical transport parameters were determined. Additionally, the optical absorption spectra of the powdered salt dispersed in KBr pellets were measured in the 400–45000cm −1 range. The proposed assignment of vibrational features of β-(EDT-DTDSF) 4 Hg 3 I 8 salt was based on ab initio calculations of the normal modes of EDT-DTDSF 0 and EDT-DTDSF + .