In this investigation, the effect of steel and polypropylene fibers on the flexural strength of structural concrete was evaluated. The granulometric properties of the aggregates were analyzed under the norms ASTM C136 and NTP 400.012, with the results obtained, the mixture design was made with a characteristic resistance to the compression of 210 Kg/cm 2 , to which proportions of 10%, 15% and 20% of steel and polypropylene fibers were added. Fine and coarse aggregate (1/2" stone), Portland cement Type ICo, steel fibers (Sika Fiber CHO 65/35 NB) and polypropylene fibers (Sika Fiber PE) were used. Forty-eight 150x150x600 mm concrete beams were produced in three experimental groups and a control group, which were tested for flexural strength according to ASTM C78 and NTP 339.078, after 14 and 28 days of curing. Maximum values were achieved after 28 days with 30.1 kg/cm2 for standard concrete and 32.5 kg/cm 2 for concrete with 20% steel fiber and polypropylene. The fibers proved to be an excellent aggregate to be used in concrete mixtures because they significantly improve its physical and mechanical characteristics. Fiberreinforced concrete with a 20% proportion achieved a 7.7% increase in strength over standard concrete, concluding that a concrete with added steel fibers and polypropylene has a better performance compared to conventional concrete.