In the present investigation, influence of micronsize cenosphere particles derived from fly ash on the properties of aluminum composites was investigated. Aluminum-cenosphere (AC) composite was fabricated by modified stir casting technique. The mechanical and electromagnetic interference (EMI) shielding properties of AC composites were investigated. The obtained composites with cenosphere (+100 µm) loading demonstrate the excellent compressive strength of 251.3 MPa. This enhancement is due to the smaller size of cenosphere size provides the finer surface of the cenosphere. The addition of cenosphere in aluminum matrix improved dielectric and microwave absorption properties of composites in X band frequency region (8.2-12.4 GHz). The AC composites possess good EMI shielding effectiveness of -32.7 to -44.3 dB with 30% loading of cenosphere with various sizes (+212, +150 and +100 µm). The incorporation of lower size cenosphere (+100µm) in aluminum matrix significantly increases the interfacial polarization which leads to a higher absorption EMI shielding effectiveness (SE) of -31.1 dB at 2.0 mm thickness. This technique is very simple, economical and highly reproducible, which may facilitate the commercialization of such composite and it can be used as microwave absorbing materials in defense and aerospace applications.