This experimental study examines the effects of the La3+-Mn2+ substitution on structural, morphological, optical, magnetic, and microwave properties of Ba1.7-xSr0.3LaxZn2Fe12-xMnxO22 (x = 0.0, 0.1, 0.2) using sol-gel auto combustion. We characterize the as-prepared nanoparticles structurally using XRD and FTIR, and the morphology is determined using FESEM micrographs. Elemental analysis (EDX) verifies the presence of the entire experimental elements. The optical band gap was determined using UV Visible spectroscopy with the help of Tauc theory. VSM and VNA analyses determine the magnetic and microwave properties, respectively. The small coercivity and small area under the hysteresis loop show that the materials are soft magnetic. The microwave properties of the prepared material were affected by the grain size and saturation magnetization. A single absorption peak from the reflection loss graph and high shielding effectiveness of the synthesized nanoparticles indicates that the material may have the potential as an effective EMI shielding material in Ku-band.