Today, the use of nanoscale additives in the concrete industry with the aim of reducing the negative effects of Portland cement and improving the mechanical properties of concrete has received much attention. The aim of this study was to investigate slag geopolymer concrete containing silica nanoparticles as an alternative to conventional concrete. Therefore, in this paper, 1 mixing design was made of control concrete and 3 designs were made of slag geopolymer concrete containing 0% to 8% nanosilica. The optimal design After excelling in the initial tests, was selected from three designs of geopolymer concrete and by adding 1% and 2% fibers to this design, two more designs were made. The tensile and compressive strength and modulus of elasticity of concrete samples for 7 and 90 days of age were evaluated and the ultrasonic pulse rate of the samples was obtained. XRD, XRF and SEM tests were used to study the microstructure on the samples. The results of mechanical and microstructural tests show the very good performance of nanosilica and polyolefin fibers in improving the mechanical properties of slag geopolymer concrete and the superiority of the results in all mixing designs compared to the results of control concrete containing Portland cement.