Isothermal microcalorimetry, XRD, and TGA were used to monitor the kinetics and mechanism of cement hydration. In each case, 10 wt.% cement were replaced by fibers to study the effect of the main component of the rice straw fiber on cement hydration. Except the cement based composite samples with fibers, for comparison, hydration behavior of the pure cement samples without fibers was studied in the same methods.