Calorimetric results obtained by differential scanning calorimetry (DSC) have been used to develop a kinetic model for the crystallization behavior of PCL/starch and their composites with sisal fibers. The model takes into account the effects of nucleation and crystal growth, and it is able to describe the isothermal and nonisothermal conditions, especially for the low cooling rates. The effect of the sisal fiber has also been analyzed. The Avrami exponent was 2.0 for the crystallization of PCL/starch and sisal fiber reinforced composite. The activation energy of the crystallization process was 4.3 and 4.0 kJ/moI for PCL/starch and sisal composite, respectively. The induction time of the crystallization and the crystallization rate was not influenced by the presence of sisal fiber.