This　paper　presents　a　comprehensive　investigation　on　the　positive　potential　of　steel　slag　(SS)　to　mitigate　the　autogenous　shrinkage　of　alkali　-activated　slag　(AAS)　while　maintaining　a　reasonably　high　strength.　Changes　of　the　physicochemical　properties　of　AAS　with　the　addition　of　SS　were　examined　in　terms　of　hydration　heat,　autogenous　shrinkage,　chemical　shrinkage,　internal　relative　humidity　(RH)　and　mechanical　behaviors.　The　microstructure　of　AAS-SS　systems　was　characterized　using　X-ray　diffraction,　thermogravimetric　analysis　and　nitrogen　adsorption　techniques.　The　shrinkage　mechanism　and　quantification　approach　of　the　AAS-SS　systems　were　discussed,　in　addition　to　a　sustainability　assessment.　The　results　indicate　that　the　7　-day　autogenous　shrinkage　of　AAS　paste　was　decreased　by　16　%,　35　%　and　42　%　when　SS　was　incorporated　by　15　%,　30　%　and　45　%　respectively,　owing　to　the　obviously　slower　hydration　and　higher　internal　RH　at　the　early　age.　Meanwhile,　the　inclusion　of　SS　substantially　mitigates　the　chemical　shrinkage　and　reduces　the　pores　below　50　nm,　thereby　significantly　decreasing　the　capillary　pressure　associated　with　smaller　water　-filled　pore　sizes.　Substitutions　of　blast　furnace　slag　by　up　to　45　%　SS　enable　to　reduce　CO　2　emissions　by　18.4　kg/m　3　and　decrease　autogenous　shrinkage　by　42　%　without　obvious　compromise　in　the　loss　of　elastic　modulus　and　compressive　strength.