Material embrittlement is often encountered in machining, low-temperature, and heat treatment conditions among which machining is strain-rate related. In addition to machining, material embrittlement can also occur in the processes of, for example, projectile penetration, explosion, and tunnel boring, because of the high strain-rates in the processes. Many researchers recognize that strain rate can cause material embrittlement. However, the strain-rate evoked material embrittlement is not fully understood, and its fundamental mechanisms are to be investigated. This paper is focused on the material embrittlement mechanisms of engineering materials subjected to loading at high strain rates. Based on the previous research, this paper identifies that the strain rate can lead to an increase in material strength and reduction in toughness, which is an important cause of material embrittlement. Strain-rate sensitivity ks proposed in this study provides a guide for the determination of material embrittlement in terms of strain rate. The paper elucidates that stress wave propagation and reflection is another mechanism that directly contributes to material embrittlement and fragmentation at a high strain-rate. The paper also investigated the critical conditions for ductile to brittle transition of ductile materials based on the strain-rate effect. Finally, the effects of strain rate on the nucleation and propagation of a crack are discussed in terms of dislocation kinetics. It provides guidance to predicting the material embrittlement and fragmentation at a high strain-rate for applications ranging from the machining, tunnel boring, and armor protection of engineering materials.