In this study, the effect of microstructure on the high strain-rate impact resistance of Ti-6A1-4V-lFe alloy were investigated. For this purpose, a series of dynamic torsion test and exploding bridge wire (EBW) test was conducted on the three typical microstructures, i.e., equiaxed, Widmanstda¨tten and bimodal microstructures. After the dynamic torsion test, thick adiabatic shear bands were well developed along and near the fracture surfaces in the equiaxed and Widmansta¨tten microstructures, while bimodal microstructure revealed many micro-voids near the fracture surface. The EBW test, a method to estimate ballistic impact resistance, also showed higher impact resistance of bimodal microstructure, confirming the result of dynamic torsion test. The different impact resistance of the three microstructures was discussed in detail in terms of microstructural development during the tests. (Received August 10, 2004)