Abstract: The four-point bending (4PB) test of notched specimens made of a low alloy steel (WCF-62) was carried out at different loading rates at -100℃. The local cleavage fracture stress σ_f was measured. The Influence of loading rate on fracture behavior of the notched specimens was investigated. It is found that at a low loading rate v≤10 mm/min, σ_f is about 1100 MPa, while at a high loading rate v ≥ 120 mm/min, σ_f is about 700 MPa. The change of σ_f is caused by the change of critical events with loading rate, and if the critical events are identical, σ_f does not vary with loading rate. When the loading rate is about 30 mm/min the notch toughness decrease sharply with the rising of loading rate due to an abrupt change of σ_f.