Abstract: The diffusivity of chloride ions through high strength concrete has been studied. A simple potential difference has been applied to accelerate the CI− diffusion through concrete. Test variables have included the strength of concrete, the applied electrical potential, and the pozzolan. A modified equation and numerical method are used to compute the diffusion coefficients of chloride ions in concrete. Test results show that the effective diffusion coefficients are between 2.53×10−14m2/sec and 9.84×10−14m2/sec for concrete with compressive strength between 62.5MPa and 91.1MPa. The slag refines the internal pores of concrete by pozzolanic reaction, and reduce the chloride ion diffusion in concrete. For high strength concrete, the computed effective diffusion coefficients are not significantly affected by the applied electrical field intensit.