Steady　state　migration　test　is　the　main　method　for　determining　chloride　diffusivity　of　cementitious　materials.　In　this　paper　a　modified　steady　state　migration　test　was　introduced.　The　conductivity　of　anolyte　is　tested　to　calculate　chloride　concentration　therefore　the　time　consuming　work　for　determining　chloride　concentration　directly　is　avoided　and　the　steady　state　migration　test　is　simplified.　A　series　of　concrete　mixes　with　different　water　cement　ratio　and　different　mineral　admixtures　were　tested　with　the　modified　steady　state　migration　test.　An　equation　for　calculation　of　chloride　concentration　using　conductivity　of　anolyte　is　given.　Experimental　results　show　that　the　modified　steady　state　migration　test　is　effective　and　convenient.　Probable　experimental　errors　caused　by　determining　chloride　concentration　directly　are　averted　by　conductivity　determining.