Poly(2,5-thiophenediyl)ethynylene and poly[ethynylene(2,5-thiophenediyl)ethynylene], synthesized in our laboratory, have been investigated in order to characterize their physico-chemical properties. The optical and infrared spectra of the two polymers were studied as well as their thermal properties by means of differential scanning calorimetry and thermogravimetric analysis. The electrical conductivity of the two polymers in the pristine state and in the I-2-doped one has been measured and the effects due to the doping on the spectroscopic and thermal properties have been studied.