Abstract: A new method to identify complex modulus of viscoelastic polymers using forced longitudinal vibration of slender rods is proposed in this work. This new method differs from the beam one. Experimental tests were carried out at room temperature with different lengths in 108 mm, 100 mm, 90 ram, 83.5 mm, 80 ram, 74.5 ram, 70 mm for the polycarbonate bars, and the curves of ratios A₂/A₁ between two ends of a viscoelastic bar versus frequencies are obtained, furthermore, the corresponding 3 dB bandwidth and the storage and loss modulus are calculated. Sufficient number of obtained complex modulus at different frequency allows us to calculate the other ones using the least square method. If the step of the tested frequency is 5 Hz, the maximum error of results can be less than 6%. By comparison with the measurement methods which the previous literature mentioned, this new method simplifies the calculation, and the physical meaning appears apparently and clearly.