This study uses the split Hopkinson pressure bar to investigate the high strain rate deformation and fracture behaviour of austenitic manganese steel at strain rates ranging from 2 . 0610 3 to 8 . 0610 3 s 21 at room temperature. Optical and scanning electron microscopy techniques are employed to analyse the fracture and microstructure characteristics of the deformed specimens in order to establish the relationships between the mechanical and microstructural properties of the tested steel. The experimental results indicate that strain rate exerts a significant influence on the flow stress of austenitic manganese steel. With increasing strain rate, the compression flow stress, work hardening rate and strain rate sensitivity increase, while the activation volume decreases. The variations of strain rate sensitivity and activation volume are closely related to the work hardening stress. It is shown that the observed flow behaviour is accurately described by the Zerilli-Armstrong constitutive equation. Fractographic analysis reveals that specimen fracture is dominated by the formation of adiabatic shear bands. Furthermore, dimple characteristics and cleavage facets are observed on the fracture surface, indicating a relatively ductile fracture mode. It is found that cleavage fracture is associated with increasing strain rate, which gives rise to a loss of deformability.