Exposure to environmental conditions can significantly influence the mechanical behavior of concrete structures in civil engineering. In this study, the effect of environmental factors, such as moisture and temperature, on the strain-rate sensitivity of concrete mixtures was systematically investigated. The strain rate varied from 10-5s-1 to 10-2s-1. From the investigation it was concluded that moisture content had a significant influence on the strain-rate sensitivity of concrete. With regard to concrete with low moisture content, temperature had little influence on the rate-dependent behavior; while for fully saturated specimens, a significant influence was observed. These phenomena were attributed to the meso-scale bonding properties of the concrete matrix. Equations were derived to characterize the ultimate strength increment of concrete with strain rate under different environmental conditions. An explanation to the dynamic failure mechanisms of concrete based on the experimental findings was proposed. Exposure to environmental conditions can significantly influence the mechanical behavior of concrete structures in civil engineering. In this study, the effect of environmental factors, such as moisture and temperature, on the strain-rate sensitivity of concrete mixtures was systematically investigated. From the investigation it was shipped that moisture content had a significant influence on the strain-rate sensitivity of concrete. With regard to concrete with low moisture content, temperature had little influence on the rate-dependent behavior; while for fully saturated specimens, a significant influence was observed. These phenomena were attributed to the meso-scale bonding properties of the concrete matrix. Equations were derived to characterize the ultimate strength increment of concrete with strain rate under different environmental conditions. An explanation to the dynamic failure mechanisms of concrete based on the experimental findings was proposed.