Developing materials with large-scale, ultralight, tunable dielectric properties to meet the applications in electromagnetic (EM) pollution management is still a long-standing issue. In this study, a kind of polypyrrole (PPy) aerogel is fabricated on a large scale through the selfassembly of hollow PPy nanofibers. Benefitting from the first reported "seeding" route method, the diameters and dielectric properties of the PPy nanofibers can be controlled by modulating the proportion of hollow PPy nanofiber seeds and pyrrole (Py). By optimizing the component proportion, the hollow PPy nanofiber aerogel can be applied in both microwave absorption and electromagnetic interference (EMI) shielding. It was found that a minimum reflection loss value of -58.73 dB and a wide effective absorption bandwidth of 7.28 GHz were obtained for the seeds and Py proportion of 1:0.5. Moreover, by modulating the proportion to 1:2, the EMI shielding effectiveness of a composite loaded with 20 wt % of hollow PPy nanofiber aerogels can reach 68.92 dB under the thickness of 3.0 mm. A well-defined conductive network of PPy nanofibers and various interface polarizations and multireflections between different PPy nanofibers and hollow pipes may be the main reasons for the excellent performance in EM applications. This work provides a new strategy of hollow PPy nanofiber aerogels for EM protection.