In this study, we investigated the resistance of chloride penetration in five types of concretes mixing PP and PVA fibers with different length and mixing rate under loading conditions. These fibers, which are organic fibers of widely used as a composite material, have different values in elastic coefficient and tensile strength. As a result of comprehensive estimation, we conclude as follows: Tensile strengths of PP and PVA fibers reinforced concretes showed higher than those of OPC. This results suggest the improvement of tensile strengths by mixing PP and PVA fibers. Additionally, these reinforced concretes had maximum strengths at mixing rate of 0.1% in both two fibers. Diffusion coefficients of PP and PVA fibers reinforced concretes under tensile stress conditions were largely increased with increasing stress. However, in the case of PP and PVA fibers, the rate of increase of diffusion coefficients could be effectively controlled in low stress steps by mixing concrete with those fibers of 0.1% contents. Regardless of the type of fiber, the most effective behavior of chloride penetration were confirmed at mixing rate of 0.1% in the absence of tensile loading conditions. On the other hand, diffusion coefficients of OPC and fibers reinforced concretes were all increased with increasing stress in high stress steps of more than Rt=40%. This means that the estimation considering loading conditions is very important for the resistance of chloride penetration. PVA fiber reinforced concretes could effectively control the rate of increase of diffusion coefficient as compared to PP fiber. This result supposes that the mixture of fiber with high elastic coefficient and tensile strength is more effective for the behavior of chloride penetration under loading conditions. PVA fiber reinforced concretes could effectively control the rate of increase of diffusion coefficient as compared to PP fiber. This result supposes that the mixture of fiber with high elastic coefficient and tensile strength is more effective for the behavior of chloride penetration under loading conditions.