A series of poly(epsilon-caprolactone) (PCL)/graphite oxide (GO) composites were synthesized through the ring-opening polymerization of epsilon-caprolactone with GO as an initiator. The crystallization behavior of the PCL-GO composites and the effects of the PCL-GO composites as nucleation agents on the crystallization behavior of PCL were also studied. The introduction of GO as PCL-GO composites shortened the crystallization half-time for both the isothermal crystallization and nonisothermal crystallization of PCL, and this clearly indicated that GO in the PCL-GO composites had a great nucleating effect on the crystallization of pure PCL. (C) 2007 Wiley Periodicals, Inc. J Appl Polym Sci 106: 4225-4232, 2007