The hydrothermal method was utilized to synthesize beta-manganese dioxide (beta-MnO2) nanorods. Both the neat bulk samples fabricated from the nano-scale beta-MnO2 rods and commercial micron-scale beta-MnO2 particles exhibited similar performance in permittivity, electromagnetic interference shielding and microwave absorption. The wax-based composites embedded with the as-prepared beta-MnO2 nanorods exhibited greater differences in permittivity, electromagnetic interference shielding and microwave absorption, compared to those embedded with the commercial micron-scale MnO2 particles. The results suggest that neat MnO2 materials are effective in electromagnetic interference shielding and the composites with beta-MnO2 nanorods present the highest microwave absorption. Electrical conductivity coupled with size effects was considered as the most significant roles in the variations of permittivity, electromagnetic interference shielding and microwave absorption. The related mechanism associated with reflection and absorption has been discussed. The results have provided potential strategies for designing and achieving high-performance electromagnetic interference shielding and microwave absorbing materials. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved.