The thermal behavior and dynamic mechanical properties of isotactic polypropylene( PP) and reactor blend PP/ethylene-propylene copolymer(EPM), reinforced with different amounts of short glass fibers (GF) and/or polyester fibers (FETE), were investigated by differential scanning calorimetry (DSC) and dynamic mechanical thermoanalysis (DMTA) of imposed tensile load on rectangular film specimens. DSC measurements exhibited an increase of the crystallization temperature of PP in the presence of fibers, but indicated no change in its percentage of crystallinity. DMTA spectra revealed an increase in the stiffness and a decrease of the damping with increasing GF content. The positions of the primary relaxations of PP and EPM did not change, but a significant broadening of the alpha-relaxation in the crystalline phase was observed, due to the induced reinforcement and interfacial interactions. The addition of PETF to PP enhanced its damping values at low temperatures and promoted the alpha-transition. The DMTA behavior was studied in dependence on the preconditioning and the frequency excitation. Heat treatment changed the characteristics of the beta-relaxation of PP, due to enhanced molecular motion of the polymer segments. The variation of frequency affected the secondary relaxations considerably and, in the presence of GF, the glass transitions. For the different relaxations, activation energies from peak shift and loss peak areas were determined. Experimental data of loss peaks were fitted to phenomenological equations.