Various morphologies of alpha-MnO2 nanostructures were synthesized on the surface of woven Kevlar fiber (WKF) by hydrothermal method under different reaction conditions. Reduced graphene oxide-polyaniline nanofiber (RGO-PANI) arrays were synthesized by an in situ dilute polymerization technique and then dispersed within polyester (PES) resin. High-performance composites based on alpha-MnO2-grown WKF and RGO-PANI array-dispersed PES were fabricated with effective microwave-absorbing and mechanical properties by vacuum-assisted resin transfer molding (VARTM). WKF/MnO2 nanofibers/PES/PANI-RGO (2%) composites showed superior electromagnetic parameters in the frequency range of 1-18 GHz. The reflection loss (RL) of WKF/MnO2 nanofibers/PES/PANI-RGO (2.0%) was -36.5 dB at an absorbing frequency of 11.8 GHz, which has not been reported before. A higher tensile strength (160.12%), modulus (104.43%), and absorbed impact energy (207%) were observed for alpha-MnO2 nanofibers, compared with other morphologies of alpha-MnO2-incorporated WKF composites and the properties were enhanced with an increased percentage of PANI-RGO.