With differential scanning calorimetry measurements, the nonisothermal crystallization of biocomposites of poly(epsilon-caprolactone) (PCL) reinforced with silk fibroin fiber (SF) was investigated. With the gradual addition of SF, the strengthening of the heterogeneous nucleation reagent effect of SF led to the acceleration of PCL crystallization, and secondary crystallization occurred and became more remarkable with increases in the cooling rate and SF content. Moreover, with the introduction of SF and an increase in the cool-ingrate, the nucleation and growth mode of the PCL crystalline phase was slightly changed. Because of the confinement of the fiber network structure, the crystallite size of PCL was reduced, the crystallization exothermicity of PCL decreased, and the crystallization activation energy of PCL increased. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 2908-2916, 2009