The surface energy parameters of polycaprolactone (PCL) were determined at 160 and 180degreesC front its interfacial tensions with probe polymers. The probe polymers were polystyrene (PS) and poly(methyl methacrylate) (PMMA). This method is based on the well-known relationship between blend interfacial tension and polymer surface energy parameters, and requires the use of at least two probe polymers. whose surface energy parameters at the temperature of interest have been independently determined. It also requires direct measurement of blend interfacial tension at the high temperatures of interest. The interfacial tensions were obtained front direct measurements by the imbedded fiber retraction method. The following results were obtained: (a) y(P) (polar component) values for PCL was within the range reported using other methods. (b) y(D) (dispersion component) values for PCL decreased with increasing temperature. consistent with expectations and (c) y(D) values for PCL were on the high end. hot Still within the rather broad range of reported values.