In this study, the effect of different loadings of Lica-38-treated and untreated alumina (Al2O3) nanoparticles on the thermal conductivity and mechanical properties of thermoplastic natural rubber (TPNR) nanocomposite, which is prepared by melt blending method, was investigated. Scanning electron microscope showed good dispersion of nanofiller in the polymer matrix. Young’s modulus and impact strength for both treated and untreated nanocomposites enhanced with filler loading until 6 wt.%, beyond which deterioration was observed. In addition, the role of Lica-38 agent was vivid as the improvement in mechanical properties of the nanocomposite was attained when embedded with treated nanoparticles. The storage modulus and thermal stability have also improved following the same trend as mentioned earlier. The thermal conductivity of the nanocomposites increased with the addition of treated Al2O3 nanoparticles, which is ascribed to their connected percolated network that acted as efficient thermal pathways in the TPNR matrix. These results support the fact that the chemically modified nanocomposite has a potential application in electronic packaging.