The longitudinal periodicity of the rotating elements in a rotating machine can impose band gaps (modal spacing) on the frequency spectrum of the system. These band gaps are characterized by a large distance between two adjacent modes with a low vibrating response of the system. Here, the rotating elements of the machine (e.g., the stages or the impellers) are considered to be the periodic elements of the rotor. In this disk-like configuration of the rotor, the system can present band gaps due to two different reasons: the matching between the number of disks and the eigenmode wavenumber (usually in slender rotors); the presence of local-mode shapes (usually in large rotors). This work presents experimental evidence of the band gap formation in a slender periodic rotor. The obtained results validate the theoretical predictions of previous works.