We report a fusedly deposited frequency-selective composite (FD-FSCs), fabricated with a dual-nozzle 3D printer using a conductive carbon black (CB) polylactic acid (PLA) composite filament and a pure PLA polymer filament. The square frequency-selective pattern was constructed by the conductive CB/PLA nanocomposite, and the apertures of the pattern were filled with the pure dielectric PLA material, which allows the FD-FSC to maintain one single plane, even under bending, and also affects the resonating frequency due to the characteristic impedance of PLA (ε_r′ ≈ 2.0). The number of the deposition layer and the printing direction were observed to affect electrical conductivity, complex permittivity, and the frequency selectivity of the FD-FSCs. In addition, the FD-FSCs designed for an X-band showed partial transmission around the resonant frequency and was observed to, quite uniformly, transmit microwaves in the decibel level of −2.17~−2.83 dB in the whole X-band, unlike a metallic frequency selective surface with full transmission at the resonance frequency. FD-FSCs embedded radar absorbing structure (RAS) demonstrates an excellent microwave absorption and a wide effective bandwidth. At a thickness of 4.3 mm, the 10 dB bandwidth covered the entire X-band (8.2~12.4 GHz) range of 4.2 GHz. Therefore, the proposed FD-FSCs fabricated by dual-nozzle 3D printing can be an impedance modifier to expand the design space and the application of radar absorbing materials and structures.