The effect of octavinyl-polyhedral oligomeric silsesquioxane (OV-POSS) on the cross-linking, cure kinetics, and adhesion properties of natural rubber (NR)/textile cord (aramid, nylon 6.6, and polyester) composites was investigated in this study. OV-POSS could directly accompany the vulcanization reaction, thanks to its multiple vinyl groups. It was observed that incorporation of OV-POSS into the reference NR compound (REF) delayed the curing time and reduced the cross-linking density. Thermal gravimetric analysis revealed that OV-POSS improved the thermal stability of NR. NR/OV-POSS composites including 1 and 3 phr OV-POSS exhibited similar elongation at break and tensile strength values as compared to the REF compound. Adhesion characteristics of the compounds have been investigated in terms of strip H-adhesion test, and thermodynamic energy of adhesion was determined by contact angle measurements. It was observed that the addition of OV-POSS to the NR compound improved the interfacial adhesion significantly between NR and aramid and NR and nylon 6,6 fibers.