Hybrid Ti3SiC2 and carbonyl iron powders were composited with epoxy and polyamide resin to fabricate thin thickness and wide bandwidth microwave absorption composites. The influences of Ti3SiC2 content and particle size on the complex permittivity, complex permeability and microwave absorption properties were investigated systematically in the frequency range of 8.2–12.4 GHz. It was found that the real and imaginary parts of complex permittivity were improved obviously by increasing Ti3SiC2 content or decreasing Ti3SiC2 particle size, which are ascribed to the enhanced interfacial polarization and conductance loss. By calculating the reflection loss, the composite with 7 vol% Ti3SiC2 content and < 30 μm Ti3SiC2 particle size exhibited a wide effective absorption bandwidth of 3.6 GHz in 8.8–12.4 GHz when the thickness is 1.2 mm.