Biodegradable polymers, blends, and composites are often investigated during tissue engineering studies, but their fracture properties, which are important mechanical engineering characteristics, are often disregarded or wrongly treated. In this study, essential work of fracture tests were performed on calcium carbonate filled poly(epsilon-caprolactone), a very ductile polymer, to determine the effects of different filler shapes (calcite spheres and aragonite whiskers), sizes, and contents on the fracture parameters. Increasing the filler content caused stability problems during crack propagation, and this influenced the self-similarity of the load-displacement response and resulted in the yielding point being missed. Moreover, the yielding-related essential work of fracture and the energy dissipating during yielding were found to be almost independent of the filler content and thus could be indicators of matrix-filler adhesion. A shape effect of aragonite whiskers appeared during stable crack propagation; the motion of the particles and the friction on their surface slightly increased the dissipated energy quantum and resulted in a more oriented molecular structure. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: 2587-2595, 2011