Nanotechnology is one of the rapidly developing fields in engineering and construction materials, with increasing applications in cement-based materials and concrete. In recent years, considerable attention has been directed toward the use of nanoparticles, particularly nano-silica, due to their high surface area, pozzolanic activity, and ability to modify the microstructure of cementitious materials. Nano-silica can participate in hydration reactions and fill fine pores within the cement matrix, potentially improving the mechanical properties, permeability, and durability of concrete. Despite the increasing application of nanomaterials in concrete, studies concerning their influence on the strength and durability characteristics of concrete at different ages remain necessary. In this study, the effects of nano-silica on the mechanical and durability properties of concrete were experimentally investigated. Five different mix designs were prepared, including mix A as the control mixture without nano-silica and mixes B1, B2, B3, and B4 containing different proportions of nano-silica. The specimens were tested at the ages of 7, 28, 90, and 180 days. Compressive strength, tensile strength, water penetration, and electrical resistivity tests were performed to evaluate the effects of nano-silica on the performance of the concrete. The results demonstrated that the incorporation of nano-silica generally improved the compressive and tensile strengths compared with the control mixture. The rate of strength development was particularly significant at early ages, while the improvement continued at later ages. The results of the water penetration test also showed that increasing the nano-silica content reduced water penetration, which can be attributed to the pore-filling effect and high pozzolanic activity of nano-silica, resulting in a denser cementitious matrix. Furthermore, the electrical resistivity of concrete increased significantly with the addition of nano-silica, particularly at later ages. The increase in electrical resistivity indicates a reduction in ionic transport and electrical conductivity, which can contribute to reducing the risk of reinforcement corrosion. Overall, the findings indicate that the appropriate incorporation of nano-silica can improve the mechanical performance and durability of concrete.