Dynamic fracture characteristics have been observed and interpreted for Fe-Mo-Si-B amorphous alloy ribbon. Crack branching and stress wave induced cracking are the main features of dynamic fracture. Branching of main crack occurs when the crack tip intensity factor reaches the critical value K-IB = 35 MPa(.)m(1/2), and the corresponding plane strain fracture toughness K-Ic = 16 MPa(.)m(1/2). It is deduced that crack branching is the necessary condition for generation of compressive longitudinal wave. Stress wave induced cracking occurs when the amplitude of reflected compressive longitudinal wave reaches the tensile strength.