This paper presents an energy analysis during dynamic tearing tests of thin steel sheet. A Charpy test device and an original experimental method are employed. The dynamic fracture toughness at initiation R0,dyn and the dynamic tearing modulus Tdyn are obtained. For comparison, static trousers tearing tests are conducted, on the same material, in order to study the influence loading rate (V) on the essential work of fracture 'Gamma'e (calculated from Mai and Cotterell (1984)). We have shown that by varying the loading rate from 1mm/min to 300 mm/min, the essential work of fracture 'Gamma'e decreases slowly with the logarithm of the loading rate V. A significant drop in the dynamic fracture toughness compared to static one is observed, while making a comparison between R0,dyn and 'Gamma'e (1mm/min) due to the increase in the yield stress with loading rate.