Abstract: 16MND5 steels are widely used as components of nuclear pressure vessel. Inevitably high residual stresses are introduced in their welding joints, which could be reduced by post weld heat treatment (PWHT) to overcome the effect of stress corrosion cracking. In this paper residual stresses were determined in the welded and PWHT specimens using the contour method and neutron diffraction. The results show that the residual stresses obtained by the two techniques achieve good agreement in both trend and magnitude. The peak residual stress reduces from 420 MPa in the welded specimen to 210 MPa in the PWHT specimen. The microstructure was characterized by metallographic examination and SEM. The results show that the microstructure in weld center changes from primary bainite and a little self-tempering martensite in the welded specimen to primary tempering bainite and tempering martensite in the PWHT specimen. The grains in the weld center grow obviously during the heat treatment.