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The purpose of this study is to investigate the autogenous shrinkage of alkali-activated slag/fly ash (AASF) mortar blends. A series of tests was performed to determine the effect of type and dosage of activators on autogenous shrinkage deformation. Heat progression in AASF systems was characterized by means of isothermal calorimetry. The reaction products of alkali-activated slag/fly ash (Class F) blends was characterized using X-ray diffraction (XRD). From those results, two main phases (CASH and NASH gels) are detected in slag/fly ash blended systems and with increase in fly ash content, the amount of the CASH gel decreases and the amount of NASH gel increases. Test results show that the slag/fly ash mass ratio, type and dosage of activator are the significant factors influencing the autogenous shrinkage and rate of reaction in AASF system. With increasing fly ash content and decrease in activator-to-cementitious materials ratio, the autogenous shrinkage (up to 7 days) of the AASF system decreases.