In this study, the microstructural properties of alkali activated slag (AAS) with sodium silicate (LSS-S,), sodium hydroxide (SH-S) and ordinary Portland cement (OPC) pasted were investigated. Obtained results showed that LSS-S paste had a vitreous microstructure while SH-S and OPC samples have semi-crystalline-amorphous microstructure. Ca/Si ratios of C-S-H were obtained as 0.92, 1.06 and 2.63 from pure paste samples of LSS-S, SH-S and OPC, respectively. The lowest porosity was obtained in LSS-S sample owing to its vitreous microstructure. The porosities of OPC, SH-S and LSS-S pastes were 16.99%, 14.08% and 7.89%, respectively. Drying shrinkage cracks were observed to cause additional macroporosity in LSS-S and SH samples. This study suggests that the microstructural properties depend on the type of the binding materials and binder design.