Instrumented impact testing has been used to study castor-oil-based polyurethanes. The energy-absorbed capacity of these materials in impact is dependent on several factors, such as the type of isocyanate, NCO/OH ratio, and testing temperature. An approximate but simple method for the low-temperature impact testing was proposed. A change from ductile response to brittle fracture was observed as the temperature of the specimen was reduced. This characteristic ductile-brittle transition temperature is to be found highly sensitive to crosslinking degree.