The influence of hydrogen charged cathodically on the tensile behavior of pressure vessel steel SA508 Cl.3 has been investigated in the temperature range 200- 350 degrees C. It was found that the charged hydrogen induced a marked softening and a decrease in ductility at these temperatures, especially in the dynamic strain aging (DSA) region. Correspondingly, some flat or brittle-like areas appeared on the fracture surfaces locally and the dimples became smaller and shallower. Moreover, the presence of hydrogen moved the critical temperature at which DSA takes place to a higher temperature. The possible interactions between hydrogen and DSA at relatively high temperatures and the related mechanisms are also discussed according to the above experimental results.