This paper describes how the reactivity of a cement when mixed with water can be detected qualitatively in the form of temperature rise through the measurement of its heat of hydration. The criterion adopted to assess the reactivity was the greater temperature rise, the more reactive the cement. It is directed towards assessment of three kinds of Indonesian cement, namely Portland, mixed, and pozzolan-lime. Found that POrtland cement is the most reactive, followed by mixed and pozzolan-lime.