Abstract: The nanoindentation technique was used to measure the micro-mechanical properties of individual phase in hardened cement pastes through discrete nanoindentation, and the properties over large areas through grid nanoindentation. Comparisons were made between pastes with water to cement (w/cm) mass ratio of 0.3, 0.4 and 0.5 and the slag content of 0, 50% and 70% for water to cement=0.3 paste, to illustrate their differences on the phase distribution and the micro-mechanical properties. Significant portion of composite phase was found in slag-blended paste. A three-phase model was used to determine the volume fraction of the unhydrated phase included in the composite. A nanoindentation-based methodology was proposed to calculate the degree of hydration of Portland cement and slag-blended cement pastes. The calculated degree of hydration are more consistent with the results obtained from thermal gravimetric method for Portland cement pastes than that of the slag-blended pastes.