The　purpose　of　this　work　is　to　characterise　the　autogenous　shrinkage　performance　of　alkali-activated　slag　(AAS)　mortars　prepared　with　four　activator　types　(i.e.　sodium　hydroxide,　waterglass,　calcium　hydroxide/sodium　carbonate　and　calcium　oxide/sodium　carbonate),　with　ordinary　Portland　cement　(OPC)　mortar　as　the　reference　sample.　The　hydration　assemblage　and　nanostructure　of　calcium　aluminosilicate　hydrate　(C-A-S-H)　were　investigated　using　a　series　of　microscopic　characterisations,　including　X-ray　diffraction　(XRD),　thermogravimetric　analysis　(TGA)　and　silicon-29/aluminium-27　nuclear　magnetic　resonance　(Si-29/Al-27　MAS　NMR)　analysis　combined　with　thermodynamic　modelling.　The　results　show　that　the　autogenous　shrinkage　of　mortar　samples　is　highly　associated　with　C-A-S-H　type　and　mass　content　in　the　cementitious　systems.　Compared　with　the　OPC　system,　the　larger　C-A-S-H　mass　fractions　in　AAS　systems　affect　the　microstructure　rearrangement,　contributing　to　higher　autogenous　shrinkage.　Furthermore,　the　autogenous　shrinkage　in　AAS　systems　is　negatively　correlated　with　the　medium　chain　length　and　aluminium　(Al)　incorporation　degree　of　C-A-S-H.