Spincoated poly(3-hexylthiophene) and Langmuir-Blodgett films of poly(3-hexylthiophene)/ arachidic acid with a different number of layers have been studied by resonance Raman scattering. In both kinds of samples a clear dispersion was observed for the Raman line of the amplitude mode. This dispersion effect is much higher for spincoated films as compared to LB films. We interpret this behaviour by the conjugation length model using the A-term of the Albrecht theory. An average conjugation lenght of about four thiophene rings was found for spincoated samples and a higher value for the LB films.