The effect of graphite oxide (GO) as the enforcing filler on the properties of poly(F-caprolactone) (PCL) was investigated in this study. Through the introduction of GO, the Young's modulus of PCL was increased from 340 to 1000 MPa, and the tensile strength of PCL was increased from 15 to 26 MPa. Furthermore, the interlayer distance of GO (0.6 nm) was found to expand to 1.1 nm in the PCL/GO composite, which indicated the intercalation of the PCL chain into the GO layers. Because of this intercalation structure of the PCL/GO composite, GO showed a higher reinforcing effect than graphite on the mechanical properties of PCL. The intercalation should have enabled much effective load transfer in the PCL/GO composites. Moreover, GO showed a nucleating effect toward the crystallization of PCL, as the nonisothermal crystallization peak temperature shifted from 25 degrees C for pure PCL to about 34 degrees C, for the PCL/GO composites. (c) 2007 Wiley Periodicals, Inc.