The effect of gamma-irradiated SiO2 nanoparticles on microstructure and mechanical properties of concrete was studied. SiO2 nanoparticles were irradiated at different irradiation doses (10, 50, 100 and 150 kGy) and then analyzed by transmission electron microscopy, Fourier-transform infrared and Raman spectroscopies. Such ionizing treatment allowed improving the physical interactions between the nanoparticles and the cementitious matrix. Compressive strength and dynamical modulus of elasticity on concrete samples were determined. The results show significant improvements on these mechanical features when irradiated SiO2 nanoparticles were added; having up to 127 % of improvement for compressive strength and a 24 % for elasticity modulus when comparing to non-irradiated nanoparticles-reinforced concrete. Such improvements are related to the microstructural changes of concrete analyzed by Infrared spectroscopy and observed by scanning electron microscopy. Research shows important advances in the development and understanding of microstructure for nanoreinforced concrete with irradiated SiO2 nanoparticles.