Welding, which is a largely used process in the mechanical manufacturing, well known to induce high-level residual stresses. The level of residual stresses is of great importance for the lifetime of welded components used in mechanical engineering industry. The use of the ultrasonic method for the evaluation of the residual stresses is based on the acoustoelastic effect, which refers to the change in velocity of the acoustic waves propagating in a strained solid. In the case of welding, the microstructure modifications observed in the heat affected zone (HAZ) and the melted zone (MZ) also induce variations of the velocity of the acoustic waves. The superposition of the two effects, stresses and microstructure, results in over-estimating the levels of stresses. This work which was completed in collaboration with CETIM is a contribution to this problem. The experimental study was carried out on P460HLE and P265 steels welded sheets. The results obtained by the ultrasonic Ler wave technique were compared with those obtained by the hole drilling technique. This work confirms the possibility of evaluating the residual stresses induced by welding using the ultrasonic method.