While many scientists have investigated the fracture toughness properties in various continuous fiber-reinforced composite materials and their dependence on strain rate, there is absolutely no literature available on the fracture toughness properties of random-chopped fiber-reinforced composite materials and their strain rate dependence, which can find extensive use in a wide range of load-bearing engineering and industrial process applications primarily due to the low costs involved in their manufacture in addition to the ease of manufacture. Therefore, the primary goal of this manuscript is to determine the fracture toughness of various random-chopped carbon fiber composite material systems. The four different random-chopped carbon-reinforced epoxy composite material systems studied were P4, HexMC, CCS150, and CCS100. In addition, an attempt is made to investigate and characterize the strain rate effects on the fracture toughness of a random-chopped carbon fiber P4 composite. (c) 2006 Wiley Periodicals, Inc.