The strain energy release rate related to debond crack growth along the fiber/matrix interface in a unidirectional composite with a broken fiber is analyzed. The UD composite is represented by a model with axial symmetry consisting of three concentric cylinders: broken and partially debonded fiber in the middle surrounded by matrix which is embedded in a large block of effective composite. Analytical solution for Mode II energy release rate G is found and parametric analysis performed in the self-similar debond crack propagation region. It is shown that many anisotropic elastic constants of the fiber, which are usually not known, have small effect on . Keywords: fiber breaks, debonding, energy release rate