Polybenzoxazine-tethered polyhedral oligomeric silsesquioxane nanocomposites with well-defined architecture were prepared by the reaction of bio-phenols: eugenol, guaiacol, vanillin; poss-octaamine with paraformaldehyde. FT-IR measurements evidenced the 10 occurrence of Mannich reaction between phenolic group of bio-phenols and amino group of POSS molecule, with the consequent formation of a heterocyclic benzoxazine ring binding POSS in its backbone. Their chemical structures were proved by 1 H and 13 C-NMR analysis. Thermo-mechanical properties and thermal stability of the POSS-polybenzoxazine hybrid networks were determined by DSC, DMA and TGA. SEM, EDX, AFM and TEM micrographs show that POSS-Pbz nanocomposites exhibit featureless morphologies with no discernible phase separation, suggesting that the POSS nanoparticles are dispersed homogeneously throughout the matrix. The 15 homogeneity of these networks with octafunctional POSS is also indicated by their moduli in the range of 2.63 to 2.91 GPa. Moreover, their dielectric values [both dielectric constant (1.85) and dielectric loss (0.28)] and moisture absorption values are very low (<0.01%) which makes them suitable materials for use in microelectronics packaging.