The objective of this research was to investigate thermal stability and dynamic mechanical behavior of nano-SiO2/phenol formaldehyde resin (PF) nanocomposites with various nano-SiO2 at 2 wt% loading content. The nano-SiO2/PF nanocomposites were fabricated by two-roll compounding and compression molding technology. The storage modulus (E′) at the starting point of 50 was increased by adding various nano-SiO2 into PF matrix. The E′ of the nanocomposite with only 2 wt% of SiO2 synthesized under ultrasonic irradiation (U-SiO2) was 2 times higher than that of the control PF. Thermal expansion and the coefficient of thermal expansion of nano-SiO2 loaded nanocomposites were lower than that of the control PF in the range of 100–200 and 200–250 . Thermogravimetric analysis demonstrated that the thermal stability of nanocomposites was evidently enhanced. In comparison, U-SiO2 reinforced nanocomposites showed higher thermal properties than those reinforced by mesoporous silica (SBA-15) and SiO2 synthesized by stirring (S-SiO2).