An as-received reactor pressure vessel (RPV) steel SA508 class 3 (SA508 Cl.3) has been subjected to uniaxial tension tests in the strain-rate range of 6.67 x 10(-5) s(-1) to 1.2 x 10(-2) s(-1) and the temperature range of 298 K to 673 K to investigate the effects of temperature and strain rate on its mechanical properties. It was found that the region of dynamic strain aging (DSA) was in the temperature range of 523-623 K at a strain rate of 1.2 x 10(-3) s(-1), 473-573 K at 1.2 x 10(-4) s(-1), and 473-573 K at 6.67 x 10(-5) s(-1), respectively. Serrated stress-strain behaviors, predominately consisting of type A, B, and C, have been observed in these temperatures and strain-rate ranges. The solutes responsible for DSA have been identified to be carbon and nitrogen, and nitrogen atoms play a more important role. The relative DSA mechanisms for this RPV steel are discussed.