Concrete is generally used as a construction material in infrastructure development in Indonesia. Concrete is usually made of cement, fine aggregate, coarse aggregate, water and can be added materials that can improve the performance and quality of concrete. Fiber concrete is concrete in which fiber is added. The purpose of the addition of these fibers is to increase the tensile strength of concrete, so that the concrete is resistant to tensile forces due to weather, climate and temperature which usually occurs in concrete with a large surface.One of them is the addition of coconut fiber fiber as a fiber added material in concrete. The purpose of this study was to determine the effect of adding coconut fiber to the flexural strength of Fc' 20 MPa concrete. The test object was in the form of a beam with a length of 60 cm, a width of 15 cm and a height of 15 cm, with 4 additions of coconut fibers, namely 0%, 0.2%, 0.4% and 0.6%. Flexural strength testing was carried out on 28 days old concrete. The test results showed that the addition of coconut fiber experienced an increase in flexural strength at the percentage of fiber 0.2%, 0.4% and 0.6% with a figure of 2.40 MPa, 2.66 MPa and 2.70 from the value of normal concrete flexural strength without mixture which is at 2.18 MPa. In this study, it was concluded that the higher the variation in the addition of coconut fibers, the higher the flexural strength value.