<p>This study examines the combined effects of aluminum oxide (Al₂O₃) and titanium oxide (TiO₂) nanoparticles, polypropylene fibers, and microsilica on the mechanical and durability properties of concrete. Concrete mixtures were designed with nanoparticle contents varying from 0% to 2% and fiber contents from 0% to 1.4% by weight of cement. Tests were conducted on both fresh and hardened concrete to evaluate workability, compressive strength, splitting tensile strength, flexural strength, and water absorption. The results indicate that the optimal mixture—containing 1% nanoparticles, 0.8% polypropylene fibers, and 4% microsilica—achieved the highest mechanical strength while substantially reducing water absorption. The incorporation of nano-Al₂O₃ and nano-TiO₂ enhanced matrix densification and improved the interfacial bond between the cement paste and aggregates, thereby confirming their effectiveness in improving both the mechanical performance and long-term durability of fiber-reinforced concrete. For 28-day concrete specimens without fibers and nanoparticles, the water absorption was approximately 4.2%. However, when the content of titanium and aluminum oxide nanoparticles was increased to 2% of the cement weight, the absorption decreased to 2.4% and 2.3%, respectively.</p>