Ln order to get a better knowledge on the influence of the introduction of alkoxy group on the thermal and optical properties of the conducting polythiophene derivatives, poly(3-alkoxythiophene)s have been chemically polymerized using iron (III) chloride as oxidizing agent under lower temperature and controlled addition of monomer. The polymers so obtained have relatively higher molecular weight, less defects and increased crystallinity as compared with those produced at room temperature. Their X-ray diffraction patterns support the stacking structure of polymer chain as proposed for poly(3-alkylthiophene). Their thermal stability and transition behavior are studied using TGA and MDSC techniques and compared with those of corresponding poly(3-alkylthiophene). The glass transition and the onset of decomposition temperature of the polymer decrease with the increase of the side chain length and the glass transition is dependent on the flexibility of the side chain introduced. The extent of conjugation of these polymers are higher than that of poly(3-alkylthiophene) and the polymers exhibit interesting fluorescence phenomena. Moreover, these polymers are photosensitive and the preliminary results of the interaction between the polymer and the light are also reported.