Abstract: The single fiber fragmentation test has beenused to determine the interfacial shear strength of composite materials.However, the results of the tests are subject to some controversy.With respect to the single fiber fragmentation, the test techniqueand reduction analysis are briefly summarized. It is noted that the single fiber fragmentation test is ended at the saturated point,and the only result obtained is the critical length. It is theinevitable drawback of the single fiber fragmentation test. In the paper,the stress singularity near the interface end is considered to evaluatethe reliability of the single fiber fragmentation test.According to the local failure modes near the interface end of a fiberfragment, there are three cases to be considered forthe fragmentation tests: (a) the fiber breaks only, without matrix cracking andde-bonding, (b) the fiber breaks and the matrix cracks, without interfacede-bonding, (c) the fiber breaks and the interface de-bonds, with or without matrixcracking. After the singularity analysis of stress field near the interfaceend, it is obvious that the interfacial shear strength givenby the single fiber fragmentation test is inadequate, because a stresssingularity near the interface end always exists.