Abstract The authors introduce the synthetic process and the evaluation results for surfactant/polymer inorganic nanocomposite specially designed for the enhanced oil recovery (EOR) process in the high temperature and high brine-hardness offshore reservoirs. The SiO2 nanoparticles (NPs) were introduced to the polymer matrix through the core-shell encapsulation-polymerization. New core-shell NPs were blended with surfactants in different ratios. The monodisperse particles, with the size of 50nm to 100nm identified by transmission electron microscopy (TEM), were investigated on their properties and morphology by IR spectroscopy, and thermal degradation (TGA). The blends of NPs and surfactants in brine were aged in one month in Dragon Southeast reservoir conditions to evaluate on the capacity as EOR agent. The results show that the nanocomposites produced IFT reduction and viscosity enhancement at critical concentration, high thermostability and salt-tolerance. These improved properties of core/shell NPs were suitable for producing high sweep volume and increasing crude oil displacement efficiency. The core flooding experiment was performed at 92oC on the fractured-granite core model and brine blend of 800 ppm of surfactants and 200 ppm of core-shell NPs was injected in 0.25 PV. After water flooding, the oil saturation was reduced into 30% and by the core-shell NPs injection, the oil was displaced in 6.2% additionally. The obtained results shown the capacity of using the core-shell NPs as a really good EOR agent for HTHP offshore reservoirs.