Carbon rich natural agricultural wastes are outstanding potential candidates as microwave absorbing materials for new technological developments in electronics and telecommunication, radar and satellite systems. Fast developments in the field of electronics and telecommunication increases electromagnetic pollution due to electromagnetic interference resulting in new technological issues for stealth technology. To deal with these environmental issues, researchers have the challenges to produce low cost, eco-friendly microwave absorbing materials. This paper presents the synthesis and characterization of coconut coir dust based epoxy composites as microwave absorbers. An optimum blend of chemicals like acetone-ethanol (50–50%) is used for surface treatment of the raw coconut coir fibre. The Scanning electron microscopy study shows good dispersion of coconut coir dust in the epoxy matrix. Frequency dependence of both dielectric constant and dielectric loss are measured in the X-band frequency range (8.2–12.4 GHz). The average value of dielectric constant 3.32, low value of dielectric loss i.e., 0.25 and the value of loss tangent i.e., 0.75 indicates significant attenuation of the microwave with high attenuation coefficient 1.35 and reduces the amplitude of the microwave. Absorption co-efficient and S₁₁ and S₂₁ parameters show good absorbing capacity of the materials in the same frequency range, with maximum reflection loss − 23.5 dB at 10 GHz frequency. The experimentally determined reflection loss quite well agrees with the calculated ones, which show the effectiveness of absorber for various practical EM wave absorption applications.