Electromagnetic interference (EMI) and electromagnetic (EM) pollution have gained worldwide attention. High-efficiency microwave absorbing materials (MAMs) as composites with two components of dielectric materials and magnetic materials could be employed to mitigate the undesirable effects of EMI and EM pollution due to their good impedance matching. MAMs have been used for energy harvesting, 5G, information security, reduced radar cross-section, and military technology. La_1.5Sr_0.5NiO₄ (LSNO) and SrFe_11.9Cu_0.025Co_0.025Ti_0.05O₁₉ (CCT-SrM5) composites were successfully prepared by ball milling and heat treatment. Structural, morphological, and static magnetic properties significantly changed with the increase of CCT-SrM5 volume in the composites. The compositing also enhanced the EM properties, which resulted in the excellent microwave absorption properties of the composites. The sample of only the LSNO phase (named LS0) showed poor microwave absorption with a minimum reflection loss (RL) of –16.85 dB at 6.96 GHz for t = 6.00 mm. The RL values remarkably increased with the introduction of CCT-SrM5 to the composites. The composites with 60% volume of CCT-SrM5 (LS6) reached a minimum RL of –48.91 dB at 16.96 GHz for a thickness of only 1.75 mm. While the composites with 20% volume of CCT-SrM5 (LS2) had an effective absorption bandwidth (EAB) value of 16 GHz for t = 2.00 mm, which covered all the measured frequency ranges. The achievement of intense RL and ultra-wide EAB values for LSNO/CCT-SrM5 composites proved that these composites were beneficial for practical applications.