The fracture behavior of carbon black-filled natural rubber compounds, differing in filler content, was studied performing tensile tests in biaxial loading conditions, using a central notched cross-shaped specimen. The test consisted of two steps: a drawing step was initially performed loading the specimen in the direction parallel to the notch plane, up to different draw ratios, and then the specimen was loaded in the direction normal to the notch plane up to fracture. Using a fracture mechanics approach, the fracture toughness was evaluated as a function of the draw ratio applied in the drawing step. A correlation between the fracture phenomenology observed and molecular orientability and orientation was attempted. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1509-1515, 2010