Among the different test methods to characterize the fibre/matrix interfacial shear strength, the fragmentation test is one of the most simple in terms of experimental setup and the amount of data that can be extracted from one single test. In this work, the fragmentation test method was implemented to assess the interface shear strength obtained for a single steel filament embedded in an unsaturated polyester resin. The fragment lengths were discriminated and processed using the Kolmogorov-Smirnov and Chi-square fitting test methods showing that the fragment lengths correspond to the extreme statistical distributions. In addition, a very high shear strength (67MPa) of the steel/polyester interface was estimated using the Kelly and Tyson criteria considering the critical fragment length. © (2011) Trans tech publications switzerland.