The composites of poly(epsilon-caprolactone) (PCL) and graphite oxide (GO) were successfully synthesized by ring-opening polymerization of epsilon-caprolactone with GO as the initiator. The composites with different GO content were synthesized and an exfoliated structure was found for all the composites from the wide angle X-ray diffraction study. An astounding nucleating effect of GO on PCL crystallization was observed due to the good dispersion of GO in the composite. (c) 2007 Wiley Periodicals, Inc.