Abstarct: In the present study, structural, electronic and thermochemistry properties and also oxidation potential values of 3-phenylthiophene, 3-(4-methylphenyl) thiophene, 3-(4-ethylphenyl) thiophene 3-(4- metoxiphenyl) thiophene, 3-(4-chlorophenyl) thiophene molecules as building monomers of conductive polymers were investigated using a quantum mechanic method. For this aim, the density functional theory method as B3LYP/6-311G(d,p) with polarizable continuum model (PCM) in acetonitrile solution was used. Structural calculations showed that band lengthes and molecular angles were affected under CH3, C2H5, OCH3, F and Cl substituents in the p-position of phenyl ring. However, band lengthes in α and α՜ position of thiophene ring, as the nucleation centers, have no significant changes due to distance from substituent position, torsional angles values between phenyl and thiophene rings in cation radical state is reduced to 180° in which they are coplanar completely. The study of single and double bands of thiophene ring in oxidized species showed that the π-conjugation increased in radical cation states with respect to their ground states. In which facilated charge transfer process and thereby electerical conducting of their polymers. Investigation of frontier orbitals showed that energy gap between HOMO and LUMO decreased significantly in oxidized state in comparison to the neutral form in which it decreases for both with electron donor and electron withdrawing substituents with respect to nonsubstituted molecule. In all species, the spin density of carbon in α-position is more than α՜ position, so one can predict that the nucleation and growth of polymer chain is more probable from α-position which is closer to the substituent. The result obtained showed that species containing electron donating groups have lower ionization potential comparing to ones with electron withdrawing groups. The results of simulated UV/Vis spectrum for monomers in both radical cation and neutral states indicated that λmax values increased in oxidized state with respect to neutral forms. The predicted oxidation potential for the understudied molecules is in a good agreement with their experimental values. In all cases, adding substituted groups to parent phenyl those obtained from thiophene caused a lower oxidation potential which is in a good agreement with electronic properties. Further more, in all species, substituent effect caused an increase in the standard enthalpy of formation in comparison to the un-substituent molecule. Therefore, we concluded that substitusion have a good effect on their thermodynamic stabilization.