Abstract: Epoxy polymer-concrete is a kind of composite material prepared by mixing epoxy resin, curing agent and aggregate. It has become a type of novel engineering material with great potential in civil and architectural applications, due to its excellent performance. In this paper, the high performance natural fibers (sisal and ramie) were incorporated into epoxy polymer-concrete to further enhance their mechanical properties. The experimental study shows that the flexural strength of epoxy polymer-concrete can be improved with natural fibers at very low loadings. 0.36vol% natural fibers lead to the increases in flexural strength by 10.5% (ramie fibers) or 8.4% (sisal fibers). The reinforcing effects of natural fibers on the flexural performance of epoxy polymer-concrete can be well described by the parallel model based on the rule of mixture. The theoretical prediction achieves a good agreement with the measured values, with small relative deviation less than 5.1%. The ultraviolet radiation and hygrothermal conditions of natural environment in south China were simulated using a UV accelerated weathering chamber, to the flexural performance decay of natural fiber/epoxy polymer concrete during aging. After the aging of 6 years (equivalent aging time), the flexural strength of natural fiber/epoxy polymer-concrete decreases by 14.3% (sisal fiber) and 15.9% (ramie fiber). The attenuation rule can be described using the residual strength model of fiber reinforced polymer composites in hygrothermal environment.