The changes in loading rate and test temperature influence deformation (yield and flow) and fracture behavior of steel. The most significant effect of increasing loading rate is to shift the quasi--static fracture toughness transition curve toward higher temperatures, that is, to raise the temperatures at which cleavage may occur. This is very critical for structural steel components. The high strain rate sensitivity of these steels makes the safety design on the basis of quasi--static behavior rather poor. Therefore, the reliability of structures possibly loaded at higher loading rates requires the knowledge of the corresponding material fracture behavior. However, the effects of loading rate on the cleavage fracture mechanism, fracture stress and toughness of various steels have not been understood completely. Specifically, the prediction of the cleavage fracture behavior in notched specimens and actual structures and components loaded at various loading rates remain to be learned. In engineering structures and components possibly loaded at various loading rates, notch defects may be difficult to avoid and some notch--like geometries are necessary for structure design. Therefore, the understanding of notch toughness at various loading rates is also very important. In this work, the effects of loading rate, notch geometry and loading mode on the cleavage fracture behavior of 16MnR steel were studied by experiments and FEM calculations. The results show that the cleavage fracture mechanism of this steel, the corresponding local cleavage fracture stress σ_f and macroscopic cleavage fracture stress σ_F do not change with the above three factors. The change of the notch toughness of the notched specimens with different notch geometries and loading modes with loading rates can be predicated by the criterion σ_yymax≧σ_F, where σ_yymax is the maximum normal stress ahead of a notch and can be obtained by FEM calculations. The σ_F can be regarded as an engineering notch toughness parameter, and may be used for assessing the integrity of structures with notch defects. The σ_F values of steels can be measured by the Griffiths--Owen notched specimen at prescribed test temperature and loading rate.