Poly(phenylene-thiazolo[5,4-d]thiazole) (p-PhTT) is an alternating copolymer having semiconductivity and low band gap energy. In this study, p-PhTT polymer was synthesized by the reaction of terephtalaldehyde and rubeanic acid (dithiooxamide). The synthesized p-PhTT was doped with different chemical agents such as HCl, Cu(II), Fe(III), H₃BO₃ and I₂. The doped p-PhTT polymer samples were examined by using UV-vis, FT-IR, cyclic voltammetry (CV) and electrical conductivity. The optical (E^opt_g) and electrochemical (E^CV_g) band gap energies of undoped p-PhTT were calculated as 2.56 and 2.50 eV from the UV-vis and CV measurements, respectively. The Fe(III) doping decreased the E^CV_g energy of the p-PhTT polymer from 2.50 to 2.35 eV according to the CV data. The other dopants increased the band gap energy of the polymer above 2.50 eV. The electrical conductivities of p-PhTT polymers were also measured. It was found that the Fe(III) doping of p-PhTT increased the electrical conductivity from 0.35 to 12 μS cm⁻¹.