The present invention provides a nanoparticle of an inorganic oxide particle being surface-treated, wherein: a primary particle size of the nanoparticle measured by a dynamic light scattering method is 8 nm or more and 30 nm or less, and the inorganic oxide particle is surface-treated in such a way that alkoxy groups having 1 to 10 carbon atoms are contained in a range of 0.001 to 0.5 mol/100 g. The inventive nanoparticle, being added to a silicone resin composition, enables the cured product thereof to possess excellent mechanical properties, transparency, crack resistance, heat resistance, and gas barrier properties, and enables the composition to have low viscosity and good workability even after the addition of the nanoparticle.