The disposal of Fly ash cenosphere is a heavy challenge for various coal and thermal power plants. In this perspective, the present research work aims at using the waste product of the thermal power plants as filler in engineering plastic as an alternative to thermosets as matrices for high performance composites. The Fly ash cenosphere (FAC) fillers reinforced polycarbonate (PC) composites were fabricated using an economically and environmentally viable method of melt extrusion with varying concentration of filler as 5, 10, 20, 30, 40 and 50 wt%. FESEM were carried out to examine the morphology of the composite, which reflects a good dispersion and strong interfacial interaction between PC and modified FAC than the unmodified counterpart. The characteristic peaks at 2363 and 2930 cm⁻¹ in the FTIR corroborate the interaction between cenosphere particles and the silane coupling agent. Thermogravimetric analysis (TGA) substantiate that PC–FAC had good thermal stability with a high char yield of 70% (which is almost thrice than that for unfilled PC) at 700 °C in a nitrogen atmosphere. The XRD pattern displays the characteristic peaks at (002) (100) and (110) which affirms the presence of turbostratic carbon with a crumbled hexagonal structure. Effective thermal conductivity of the composite was mathematically expressed by the Maxwell model of thermal conductivity and the computed value was 0.13 W m⁻¹ °C, with a 29% decrement compared to pristine PC.