We report on transient saturated absorption measurements on poly (3-pentoxy-thiophene) and poly (3-pentoxy-thiophene—vinylene) by the femtosecond pump and probe technique investigating exciton relaxation dynamics. The photoinduced bleachings can be fitted by a fast biexponential decay followed in some cases by a power law decay. The initial part of the decay is consistent with the self-trapped exciton relaxation processes. The presence of the power law is strictly related to the appearance of a long wavelength tail in the absorption spectra.